💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc2301.txt captured on 2023-01-29 at 06:55:45.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Network Working Group L. McIntyre
Request for Comments: 2301 Xerox Corporation
Category: Standards Track S. Zilles
Adobe Systems, Inc.
R. Buckley
Xerox Corporation
D. Venable
Xerox Corporation
G. Parsons
Northern Telecom
J. Rafferty
Human Communications
March 1998
File Format for Internet Fax
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
This document describes the TIFF (Tag Image File Format)
representation of image data specified by the ITU-T Recommendations
for black-and-white and color facsimile. This file format
specification is commonly known as TIFF-FX. It formally defines
minimal, extended and lossless JBIG modes (Profiles S, F, J) for
black-and-white fax, and base JPEG, lossless JBIG and Mixed Raster
Content modes (Profiles C, L, M) for color and grayscale fax. These
modes or profiles correspond to the content of the applicable ITU-T
Recommendations. Files formatted according to this specification use
the image/tiff MIME Content Type.
McIntyre, et. al. Standards Track [Page 1]
RFC 2301 File Format for Internet Fax March 1998
Table of Contents
1. INTRODUCTION........................................................4
1.1. Scope..........................................................5
1.2. Approach.......................................................5
1.3. Overview of this draft.........................................5
2. TIFF and Fax........................................................7
2.1. TIFF Overview..................................................7
2.1.1. File Structure.............................................7
2.1.2. Image Structure............................................9
2.1.3. TIFF File Structure for Fax Applications..................10
2.2 TIFF Fields for All Fax Applications...........................11
2.2.1. TIFF Fields required for all fax modes....................12
2.2.2. Additional TIFF Fields required for all fax modes.........13
2.2.3. TIFF Fields recommended for all fax modes.................15
2.2.4. New TIFF Fields recommended for fax modes.................16
3. Minimal Black-and-White Fax Mode...................................18
3.1. Overview......................................................18
3.2. Required TIFF Fields..........................................18
3.2.1 Baseline Fields............................................18
3.2.2 Extension Fields...........................................20
3.2.3 New Fields.................................................20
3.3. Recommended TIFF Fields.......................................20
3.4. End of Line (EOL) and Return to Control (RTC).................20
3.4.1 RTC Exclusion..............................................21
3.5. File Structure................................................22
3.6. Minimal Black-and-White Mode Summary..........................23
4. Extended Black-and-White Fax Mode..................................24
4.1. TIFF-F Overview...............................................25
4.2. Required TIFF Fields..........................................26
4.2.1. Baseline Fields...........................................26
4.2.2. Extension Fields..........................................28
4.2.3. New Fields................................................29
4.3. Recommended TIFF Fields.......................................29
4.3.1. Baseline Fields...........................................29
4.3.2. Extension Fields..........................................29
4.3.3. New Fields................................................29
4.4. Technical Implementation Issues...............................30
4.4.1. Strips....................................................30
4.4.2. Bit Order.................................................31
4.4.3. Multi-Page................................................31
4.4.4. Compression...............................................31
4.4.5. Example Use of Page-quality Fields........................32
4.4.6. Practical Guidelines for Writing and Reading Multi-Page
TIFF-F Files..............................................33
4.4.7. Use of TIFF-F for Streaming Applications..................34
4.5. Implementation Warnings.......................................34
4.5.1. Uncompressed Data.........................................34
McIntyre, et. al. Standards Track [Page 2]
RFC 2301 File Format for Internet Fax March 1998
4.5.2. Encoding and Resolution...................................35
4.5.3. EOL byte-aligned..........................................35
4.5.4. EOL.......................................................36
4.5.5. RTC Exclusion.............................................36
4.5.6. Use of EOFB for T.6 Compressed Images.....................37
4.6. Example Use of TIFF-F.........................................37
4.7. Extended Black-and-white Fax Mode Summary.....................37
5. Lossless JBIG Black-and-White Fax Mode.............................39
5.1. Overview......................................................40
5.2. Required TIFF Fields..........................................40
5.2.1. Baseline Fields...........................................40
5.2.2. Extension Fields..........................................40
5.2.3. New Fields................................................41
5.3. Recommended TIFF Fields.......................................41
5.4. Lossless JBIG Black-and-White Mode Summary....................41
6. Base Color Fax Mode................................................43
6.1. Overview......................................................43
6.2. Required TIFF Fields..........................................43
6.2.1. Baseline Fields...........................................43
6.2.2. Extension Fields..........................................45
6.2.3. New Fields................................................46
6.3. Recommended TIFF Fields.......................................47
6.4. Base Color Fax Mode Summary...................................47
7. Lossless Color Mode................................................49
7.1. Overview......................................................50
7.1.1. Color Encoding............................................50
7.1.2. JBIG Encoding.............................................50
7.2. Required TIFF Fields..........................................51
7.2.1. Baseline Fields...........................................51
7.2.2. Extension Fields..........................................52
7.2.3. New Fields................................................53
7.3. Recommended TIFF Fields.......................................53
7.4. Lossless Color Fax Mode Summary...............................53
8. Mixed Raster Content Mode..........................................55
8.1 Overview.......................................................55
8.1.1. MRC 3-layer model.........................................55
8.1.2. A TIFF Representation for the MRC 3-layer model...........56
8.2. Required TIFF Fields..........................................58
8.2.1. Baseline Fields...........................................58
8.2.2. Extension Fields..........................................59
8.2.3. New Fields................................................60
8.3. Recommended TIFF Fields.......................................62
8.4. Rules and Requirements for Images.............................62
8.5. MRC Fax Mode Summary..........................................63
9. MIME content-type image/tiff.......................................66
9.1 Refinement of MIME content-type image/tiff for Facsimile
Applications...................................................66
10. Security Considerations...........................................67
McIntyre, et. al. Standards Track [Page 3]
RFC 2301 File Format for Internet Fax March 1998
11. References........................................................67
12. Authors' Addresses................................................69
Annex A: Summary of TIFF Fields for Internet Fax .....................70
Annex B. IANA Registration for image/tiff Application Parameter
Values used for facsimile....................................75
Full Copyright Statement..............................................77
1. Introduction
This document describes the use of TIFF (Tag Image File Format) to
represent the data content and structure generated by the current
suite of ITU-T Recommendations for Group 3 facsimile. These
Recommendations and the TIFF fields described here support the
following facsimile modes or profiles:
S: minimal black-and-white mode, using binary MH compression
[T.4]
F: extended black-and-white mode, using binary MH, MR and MMR
compression [T.4, T.6]
J: lossless JBIG black-and-white mode, with JBIG compression
[T.85, T.82]
C: lossy color and grayscale mode, using JPEG compression
[T.42, T.81]
L: lossless color and grayscale mode, using JBIG compression
[T.43, T.82]
M: mixed raster content mode [T.44], using a combination of
existing compression methods
Each profile corresponds to the content of ITU-T Recommendations
shown and is a subset of the full TIFF for facsimile specification.
Profile S describes a minimal interchange set of fields, which will
guarantee that, at least, binary black-and-white images will be
supported. Implementations are required to support this minimal
interchange set of fields.
With the intent of specifying a file format for Internet Fax, this
draft:
1. specifies the structure of TIFF files for facsimile data,
2. defines ITU fax-compatible values for existing TIFF fields,
3. defines new TIFF fields and values required for compatibility
with ITU color fax.
This specification of TIFF for facsimile is known as TIFF-FX.
McIntyre, et. al. Standards Track [Page 4]
RFC 2301 File Format for Internet Fax March 1998
1.1 Scope
This document defines a TIFF-based file format specification for
enabling standardized messaging-based fax over the Internet. It
specifies the TIFF fields and field values required for compatibility
with the existing ITU-T Recommendations for Group 3 black-and-white,
grayscale and color facsimile. TIFF has historically been used for
handling fax image files in applications such as store-and-forward
messaging. Implementations that support this file format
specification for import/export may elect to support it as a native
format. This document recommends a TIFF file structure that is
compatible with low-memory and page-level streaming implementations.
Unless otherwise noted, the current TIFF specification [TIFF] and
selected TIFF Technical Notes [TTN1, TTN2] are the primary references
for describing TIFF and defining TIFF fields. This document is the
primary reference for defining TIFF field values for fax
applications.
1.2 Approach
The basic approach to using TIFF for facsimile data is to insert the
compressed fax image data in a TIFF file and use TIFF fields to
encode the parameters that describe the image data. These fields will
have values that comply with the ITU-T Recommendations. The MIME
content type of the resulting file will be image/tiff, with an
optional Application parameter [TIFF-REG]; see Section 9.
This approach takes advantage of TIFF features and structures that
bridge the data formats and performance requirements of both legacy
fax machines and host-based fax applications. TIFF constructs for
pages, images, and strips allow a TIFF file to preserve the fax data
stream structure and the performance advantages that come with it. A
TIFF-based approach also builds on an established base of users and
implementors and ensures backward compatibility with existing TIFF-
based IETF proposals and work in progress for Internet fax.
1.3 Overview of this draft
Section 2 gives an overview of TIFF. Section 2.1 describes the
structure of TIFF files, including general guidelines for structuring
multi-page TIFF files. Section 2.2 lists the TIFF fields that are
required or recommended for all fax modes. The TIFF fields used only
by specific fax modes are described in Sections 3-8, which describe
the individual fax modes. These sections also specify the ITU-
compatible field values (image parameters) for each mode.
McIntyre, et. al. Standards Track [Page 5]
RFC 2301 File Format for Internet Fax March 1998
The full set of permitted fields of TIFF for facsimile are included
in the current TIFF specification, Section 2 of this document and the
sections on specific modes of facsimile operation. This document
defines profiles of TIFF for facsimile, where a profile is a subset
of the full set of permitted fields and field values of TIFF for
facsimile.
Section 3 defines the minimal black-and-white facsimile mode (Profile
S), which is required in all implementations. Section 4 defines the
extended black-and-white fax mode (Profile F), which provides a
standard definition of TIFF-F. Section 5 describes the lossless
black-and-white mode using JBIG compression (Profile J). Section 6
defines the base color mode, required in all color implementations,
for the lossy JPEG representation of color and grayscale facsimile
data (Profile C). Section 7 defines the lossless JBIG color and
grayscale facsimile mode (Profile L) and Section 8 defines the Mixed
Raster Content facsimile mode (Profile M). Each of these sections
concludes with a table summarizing the required and recommended
fields for each mode and the values they can have.
Section 9 describes the MIME content type image/tiff and the use of
the optional Application parameter in connection with TIFF for
facsimile. Sections 10, 11, 12 and 13 give Security Considerations,
the ISOC Copyright Notice, References and Authors' Addresses. Annex A
gives a summary of the TIFF fields used or defined in this document
and provides a convenient reference for implementors.
To implement only the minimal interchange black-and-white set of
fields and values (Profile S), one need read only Sections 1, 2, 3, 9
and 10.
The following tree diagram shows the relationship among profiles and
between profiles and coding methods.
S (MH)
/ \
B&W / \ Color
------------ ----------
/ \ \
/ F (MMR, MR) C (JPEG)
/ / \
J (JBIG) ---- \
/ \
L (JBIG) \
\
M (MRC)
A profile is based on a collection of ITU-T facsimile coding methods.
McIntyre, et. al. Standards Track [Page 6]
RFC 2301 File Format for Internet Fax March 1998
For example, Profile S, the minimal mode, is based on Modified
Huffman (MH) compression, which are defined in ITU-T Rec. T.4.
Profile F specifies Modified Read (MR) and Modified Modified Read
(MMR) compressions, which are defined in ITU-T Rec. T.4 and T.6.
All implementations of TIFF for facsimile MUST implement Profile S,
which is the root node of the tree. All color implementations of TIFF
for facsimile MUST implement Profile C. The implementation of a
particular profile MUST also implement those profiles on the path
that connect it to the root node, and MAY optionally implement
profiles not on the path connecting it to the root node. For example,
an implementation of Profile M must also implement Profiles C and S,
and may optionally implement Profile F, J or L. For another example,
an implementation of Profile C must also implement Profile S, and may
optionally implement Profile F or J.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [REQ].
2. TIFF and Fax
2.1. TIFF Overview
TIFF provides a means for describing, storing and interchanging
raster image data. A primary goal of TIFF is to provide a rich
environment within which applications can exchange image data. The
current TIFF specification [TIFF] defines a commonly used, core set
of TIFF fields known as Baseline TIFF. The current specification and
TIFF Technical Notes 1 and 2 [TTN1, TTN2] define several TIFF
extensions. The TIFF- based specification for fax applications uses a
subset of Baseline TIFF fields, with selected extensions, as
described in this document. In a few cases, this document defines new
TIFF fields specifically for fax applications.
2.1.1. File Structure
TIFF is designed for raster images, which makes it a good match for
facsimile documents, which are multi-page raster images. Each raster
image consists of a number of rows or scanlines, each of which has
the same number of pixels, the unit of sampling. Each pixel has at
least one sample or component (exactly one for black-and-white
images).
A TIFF file begins with an 8-byte image file header. The first two
bytes describe the byte order used within the file. Legal values are
"II" (0x4949) when bytes are ordered from least to most significant
(little- endian), and "MM" (0x4D4D), when bytes are ordered from most
McIntyre, et. al. Standards Track [Page 7]
RFC 2301 File Format for Internet Fax March 1998
to least significant (big-endian) within a 16- or 32-bit integer.
Either byte order can be used, except in the case of the minimal
black-and-white mode, which SHALL use value "II". The next two bytes
contain the value 42 that identifies the file as a TIFF file and is
ordered according to the value in the first two bytes of the header.
The last four bytes give the offset that points to the first image
file directory (IFD). This and all other offsets in a TIFF file are
with respect to the beginning of the TIFF file. An IFD can be at any
location in the file after the header but must begin on a word
boundary.
An IFD is a sequence of tagged fields, sorted in ascending order by
tag value. An IFD consists of a 2-byte count of the number of fields,
a sequence of field entries and a 4-byte offset to the next IFD. The
fields contain information about the image and pointers to the image
data. Each separate raster image in the file is represented by an
IFD.
Each field entry in an IFD has 12 bytes and consists of a 2-byte Tag,
2 bytes identifying the field type (e.g. short, long, rational,
ASCII), 4 bytes giving the count (number of values or offsets), and 4
bytes that either contain the offset to a field value stored outside
the IFD, or, based on the type and count, the field value itself.
Resolution and metadata such as dates, names and descriptions are
examples of "long" field values that do not fit in 4 bytes and
therefore use offsets in the field entry. Details are given in the
TIFF specification [TIFF].
A TIFF file can contain more than one IFD, where each IFD is a
subfile whose type is given in the NewSubfileType field. Multiple
IFDs can be organized either as a linked list, with the last entry in
each IFD pointing to the next IFD (the pointer in the last IFD is 0),
or as a tree, using the SubIFDs field in the primary IFD [TTN1]. The
SubIFDs field contains an array of pointers to child IFDs of the
primary IFD.
Child IFDs describe related images, such as reduced resolution
versions of the primary IFD image. The same IFD can point both to a
next IFD and to child IFDs, and child IFDs can themselves point to
other IFDs.
All fax modes represent a multi-page fax image as a linked list of
IFDs, with a NewSubfileType field containing a bit that identifies
the IFD as one page of a multi-page document. Each IFD has a
PageNumber field, identifying the page number in ascending order,
starting at 0 for the first page. While a Baseline TIFF reader is not
McIntyre, et. al. Standards Track [Page 8]
RFC 2301 File Format for Internet Fax March 1998
required to read any IFDs beyond the first, an implementation that
reads the files that comply with this specification SHALL read
multiple IFDs. Only the Mixed Raster Content fax mode, described in
Section 8, requires the use of child IFDs.
The following figure illustrates the structure of a multi-page TIFF
file.
+-----------------------+
| Header |------------+
+-----------------------+ | First IFD
| IFD (page 0) |<-----------+ Offset
+---| |------------+
Value | +-----------------------+ |
Offset +-->| Long Values |--+ |
+-----------------------| | Strip |
| Image Data |<-+ Offset |
| strip 1 page 0 | | |
+-----------------------+ | |
| : | : |
|
+-----------------------+ | Next IFD
| IFD (page 1) |<-----------+ Offset
+---| |------------+
Value | +-----------------------+ |
Offset +-->| Long Values |--+ |
+-----------------------| | Strip |
| Image Data |<-+ Offset |
| strip 1 page 1 | | |
+-----------------------+ | |
| strip 2 page 1 |<-+ |
+-----------------------+ | |
| : | : |
|
+-----------------------+ | Next IFD
| IFD (page 2) |<-----------+ Offset
| : |
2.1.2 Image Structure
An IFD stores an image as one or more strips, as shown in the
preceding figure. A strip consists of 1 or more scanlines (rows) of
raster image data in compressed form. An image may be stored in a
single strip or may be divided into several strips, which would
require less memory to buffer. (Baseline TIFF recommends about 8k
bytes per strip, but existing fax usage is typically one strip per
image.)
McIntyre, et. al. Standards Track [Page 9]
RFC 2301 File Format for Internet Fax March 1998
Each IFD requires three strip-related fields: StripOffsets,
RowsPerStrip and StripByteCounts. The StripOffsets field is an array
of pointers to the strip or strips that contain the actual image
data. The StripByteCounts field gives the number of bytes in each
strip after compression. TIFF requires that each strip, except the
last, contain the same number of scanlines, which is given in the
RowsPerStrip field. This document introduces the new StripRowCounts
field that allows a variable number of scanlines per strip, which is
required by the Mixed Raster Content fax mode (Section 8).
Image data is stored as uninterpreted, compressed image data streams
within a strip. The formats of these streams follow the ITU-T
Recommendations. The Compression field in the IFD indicates the type
of compression, and other TIFF fields in the IFD describe image
attributes, such as color encoding and spatial resolution.
Compression parameters are stored in the compressed data stream,
rather than in TIFF fields. This makes the TIFF representation and
compressed data format specification independent of each another.
This approach, modeled on [TTN2], allows TIFF to gracefully add new
compression schemes as they become available.
Some attributes can be specified both in the compressed data stream
and within a TIFF field. It is possible that the two values will
differ. When this happens for values required to interpret the data
stream, then the values in the data stream take precedence. For
informational values that are not required to interpret the data
stream, such as author name, then the TIFF field value takes
precedence.
2.1.3 TIFF File Structure for Fax Applications
The TIFF specification has a very flexible file structure, which does
not specify the ordering of IFDs, field values and image data in a
file. Individual applications may require or recommend an ordering.
This specification recommends that when using a TIFF file for
facsimile, A multi-page fax document SHOULD be represented as a
linked list of IFDs. It also recommends that a TIFF file for
facsimile SHOULD order pages in a TIFF file in the same way that they
are ordered in a fax data stream. In a TIFF file, a page consists of
several elements: one or more IFDs (including subIFDs), long field
values that are stored outside the IFDs, and image data (in one or
more strips).
The minimal black-and-white mode (Profile S) specifies a required
ordering of pages and elements within a page (Section 3.5). The
extended black-and-white mode (Profile F) provides guidelines for
ordering pages and page elements (Section 4.4.6). Other profiles
McIntyre, et. al. Standards Track [Page 10]
RFC 2301 File Format for Internet Fax March 1998
SHOULD follow these guidelines. This recommendation is intended to
simplify the implementation of TIFF writers and readers in fax
applications and the conversion between TIFF file and fax data stream
representations. However, for interchange robustness, readers SHOULD
be prepared to read TIFF files whose structure is consistent with
[TIFF], which supports a more flexible file structure than is
recommended here.
This specification introduces an optional new GlobalParametersIFD
field, defined in Section 2.2.4. This field has type IFD and
indicates parameters describing the fax session. While it is often
possible to obtain these parameters by scanning the file, it is
convenient to make them available together in one place for fast and
easy access. If the GlobalParametersIFD occurs in a TIFF file, it
SHOULD be located in the first IFD, immediately following the 8-byte
image file header.
2.2 TIFF Fields for All Fax Applications
The TIFF specification [TIFF] is organized as a baseline set and
several extensions, including technical notes [TTN1, TTN2] that will
be incorporated in the next release of TIFF. The baseline and
extensions have required and optional fields.
Facsimile applications require (and recommend) a mixture of baseline
and extensions fields, as well as some new fields that are not part
of the TIFF specification and that are defined in this document. This
sub- section lists the fields that are required or recommended for
all modes. In particular, Section 2.2.1 lists the fields that are
required by all modes and that have values that do not depend on the
mode. Section 2.2.2 lists the fields that are required by all modes
and that have values which do depend on the mode. Section 2.2.3 lists
the fields that are recommended for all modes. Fields that are
required or recommended by some but not all modes are given in the
section (Section 3-8) that describes that mode. The sections for each
fax mode have sub-sections for required and recommended fields; each
sub-section organizes the fields according to whether they are
baseline, extension or new.
The fields required for facsimile have only a few legal values,
specified in the ITU-T Recommendations. Of these legal values, some
are required and some are optional, just as they are required
(mandatory) or optional in fax implementations that conform to the
ITU-T Recommendations. The required and optional values are noted in
the sections on the different fax modes.
McIntyre, et. al. Standards Track [Page 11]
RFC 2301 File Format for Internet Fax March 1998
This section describes the fields required or recommended by all fax
modes. The pattern for the description of TIFF fields in this draft
is:
FieldName(TagValueInDecimal) = allowable values. TYPE
WhetherRequiredByTIFForTIFFforFAX
Count = (omitted if =1) = (if not in current spec but available)
Explanation of the field, how it's used, and the values it can have.
Default value, if any, as specified in [TIFF]
When a field's default value is the desired value, that field may be
omitted from the relevant IFD unless specifically required by the
text of this specification.
2.2.1. TIFF fields required for all fax modes
The TIFF fields listed in this section SHALL be used by all fax
modes, but have field values that are not specified by the ITU
standards, i.e. the fields do not depend on the mode. The next sub-
section lists the fields that SHALL be used by all fax modes, but
which do have values specified by the ITU-specified or mode-specific
values. Fields that SHALL be used by some but not all modes are given
in the sections (3-8) which describe the modes that uses them.
ImageLength(257) SHORT or LONG
RequiredByTIFFBaseline
Total number of scanlines in image.
No default, must be specified.
PageNumber(297) SHORT
RequiredByTIFFforFAX, TIFFExtension
Count = 2
The first number represents the page number (0 for the first page);
the second number is the total number of pages in the document. If
the second value is 0, then the total page count is not available.
No default, must be specified
RowsPerStrip(278) SHORT or LONG
RequiredByTIFFBaseline
The number of scanlines per TIFF strip, except for the last strip.
For a single strip image, this is the same as the value of the
ImageLength field.
Default = 2**32 - 1 (meaning all scanlines in one strip)
StripByteCounts(279) SHORT or LONG
RequiredByTIFFBaseline
Count = number of strips
For each strip, the number of bytes in that strip after compression.
McIntyre, et. al. Standards Track [Page 12]
RFC 2301 File Format for Internet Fax March 1998
No default, must be specified.
StripOffsets(273) SHORT or LONG
RequiredByTIFFBaseline
Count = number of strips
For each strip, the byte offset from the beginning of the file to
the start of that strip.
No default, must be specified.
2.2.2 Additional TIFF fields required for all fax modes
The TIFF fields listed in this section SHALL be used by all fax
modes, but the values associated with them depend on the mode being
described and the associated ITU Recommendations. Therefore, only the
fields are defined here; the values applicable to a particular fax
mode are described in Sections 3-8. Fields that SHALL be used by some
but not all modes are given in the section (3-8) describing the mode
that uses them.
BitsPerSample(258) SHORT
RequiredByTIFFBaseline
Number of bits per image sample
Default = 1 (field may be omitted if this is the value)
Compression(259) SHORT
RequiredByTIFFBaseline
Compression method used for image data
Default = 1 (no compression, so may not be omitted for FAX)
FillOrder(266) SHORT
RequiredByTIFFforFax
The default bit order in Baseline TIFF per [TIFF] is indicated by
FillOrder=1, where bits are not reversed before being stored.
However, TIFF for Fax typically utilizes the setting of FillOrder=2,
where the bit order within bytes is reversed before storage (i.e.,
bits are stored with the Least Significant Bit first).
Default = 1 (field may be omitted if this is the value)
Facsimile data appears on the phone line in bit-reversed order
relative to its description in the relevant ITU compression
Recommendation. Therefore, a wide majority of facsimile
implementations choose this natural order for storage. Nevertheless,
all readers conforming to this specification must be able to read
data in both bit orders.
ImageWidth(256) SHORT or LONG
RequiredByTIFFBaseline
The number of pixels (columns) per scanline (row) of the image
No default, must be specified.
McIntyre, et. al. Standards Track [Page 13]
RFC 2301 File Format for Internet Fax March 1998
NewSubFileType(254) LONG
RequiredByTIFFforFAX
A general indication of the kind of data contained in this IFD
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on, so may not be omitted for FAX)
PhotometricInterpretation(262) SHORT
RequiredByTIFFBaseline
The color space of the image data
No default, must be specified
ResolutionUnit(296) SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) SHORT
RequiredByTIFFBaseline
The number of color components per pixel; SamplesPerPixel is 1 for a
black-and-white, grayscale or indexed (palette) image.
Default =1 (field may be omitted if this is the value)
XResolution(282) RATIONAL
RequiredByTIFFBaseline
The horizontal resolution of the image in pixels per resolution
unit. The ITU-T Recommendations for facsimile specify a small number
of horizontal resolutions: 100, 200, 300, 400 pixels per inch, and
80, 160 pixels per centimeter (or 204, 408 pixels per inch). The
allowed XResolution values for each mode are given in the section
defining that mode. Per [T.4], it is permissible for applications to
treat the following XResolution values as being equivalent: <204,
200> and <400,408> in pixels/inch. These equivalencies were allowed
by [T.4] to permit conversions between inch and metric based
facsimile terminals.
TIFF for Facsimile Writers SHOULD express XResolution in inch based
units, for consistency with historical practice and to maximize
interoperability. See the table below for information on how to
convert from an ITU-T metric value to its inch based equivalent
resolution.
No default, must be specified
YResolution(283) RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image in pixels per resolution unit.
The ITU-T Recommendations for facsimile specify a small number of
vertical resolutions: 100, 200, 300, 400 pixels per inch, and 38.5,
77, 154 pixels per centimeter (or 98, 196, 391 pixels per inch). The
allowed YResolution values for each mode are given in the section
McIntyre, et. al. Standards Track [Page 14]
RFC 2301 File Format for Internet Fax March 1998
defining that mode. Per [T.4], it is permissible for applications to
treat the following YResolution values as being equivalent: <98,
100>, <196, 200>, and <391, 400> in pixels/inch. These equivalencies
were allowed by [T.4] to permit conversions between inch and metric
based facsimile terminals. TIFF for Facsimile Writers SHOULD express
YResolution in inch based units, for consistency with historical
practice and to maximize interoperability. See the table below for
information on how to convert from an ITU-T metric value to its inch
based equivalent resolution. No default, must be specified
+-----------------------------+-----------------------------+
| XResolution | YResolution |
+--------------+--------------+--------------+--------------+
|ResolutionUnit|ResolutionUnit|ResolutionUnit|ResolutionUnit|
| =2 (inch) | =3 (cm) | =2 (inch) | =3 (cm) |
+--------------+--------------+--------------+--------------+
| 100 | | 100 | |
+--------------+--------------+--------------+--------------+
| 204 | 80 | 98 | 38.5 |
| 200 | | 100 | |
+--------------+--------------+--------------+--------------+
| 204 | 80 | 196 | 77 |
| 200 | | 200 | |
+--------------+--------------+--------------+--------------+
| 204 | 80 | 391 | 154 |
+--------------+--------------+--------------+--------------+
| 300 | | 300 | |
+--------------+--------------+--------------+--------------+
| 408 | 160 | 391 | 154 |
| 400 | | 400 | |
+--------------+--------------+--------------+--------------+
2.2.3 TIFF fields recommended for all fax modes
The TIFF fields listed in this section MAY be used by all fax modes.
However, Profile S writers (the minimal fax mode described in Section
3) SHOULD NOT use these fields. Recommended fields that are mode-
specific are described in Sections 3-8.
DateTime(306) ASCII
OptionalInTIFFBaseline
Date/time of image creation in 24-hour format "YYYY:MM:DD HH:MM:SS".
No default.
DocumentName(269) ASCII
OptionalInTIFFExtension(DocumentStorageAndRetrieval)
The name of the scanned document. This is a TIFF extension field,
not a Baseline TIFF field.
McIntyre, et. al. Standards Track [Page 15]
RFC 2301 File Format for Internet Fax March 1998
No default.
ImageDescription(270) ASCII
OptionalInTIFFBaseline
A string describing the contents of the image.
No default.
Orientation(274) = 1-8. SHORT
OptionalinTIFFBaseline
1: 0th row represents the visual top of the image; the 0th column
represents the visual left side of the image. See the current TIFF
spec [TIFF] for further values; Baseline TIFF only requires value=1.
Default = 1.
Note: It is recommended that a writer that is aware of the
orientation will include this field to give a positive indication of
the orientation, even if the value is the default. If the
Orientation field is omitted, the reader SHALL assume a value of 1.
Software(305) ASCII
OptionalInTIFFBaseline
The optional name and release number of the software package that
created the image.
No default.
2.2.4 New TIFF fields recommended for fax modes
The new TIFF fields listed in this section MAY be used by all fax
modes, but their support is not expected for the minimal fax mode
described in Section 3. In addition, support for these new TIFF
fields has not been included in historical TIFF-F readers described
in Section 4 and [TIFF- F]. These fields describe "global" parameters
of the fax session that created the image data. They are optional,
not part of the current TIFF specification, and are defined in this
document.
The first new field, GlobalParametersIFD, is an IFD that contains
global parameters and is located in a Primary IFD.
GlobalParametersIFD (400) IFD
An IFD containing global parameters. It is recommended that a TIFF
writer place this field in the first IFD, where a TIFF reader would
find it quickly.
Each field in the GlobalParametersIFD is a TIFF field that is legal
in any IFD. Required baseline fields should not be located in the
GlobalParametersIFD, but should be in each image IFD. If a conflict
exists between fields in the GlobalParametersIFD and in the image
IFDs, then the data in the image IFD shall prevail.
McIntyre, et. al. Standards Track [Page 16]
RFC 2301 File Format for Internet Fax March 1998
Among the GlobalParametersIFD entries is a new ProfileType field
which generally describes information in this IFD and in the TIFF
file.
ProfileType(401) LONG
The type of image data stored in this IFD.
0 = Unspecified
1 = Group 3 fax
No default
The following new global fields are defined in this document as IFD
entries for use with fax applications.
FaxProfile(402) = 0 - 6. BYTE
The profile that applies to this file; a profile is subset of the
full set of permitted fields and field values of TIFF for facsimile.
The currently defined values are:
0: does not conform to a profile defined for TIFF for facsimile
1: minimal black & white lossless, Profile S
2: extended black & white lossless, Profile F
3: lossless JBIG black & white, Profile J
4: lossy color and grayscale, Profile C
5: lossless color and grayscale, Profile L
6: Mixed Raster Content, Profile M
CodingMethods(403) LONG
This field indicates which coding methods are used in the file. A
bit value of 1 indicates which of the following coding methods is
used:
Bit 0: unspecified compression,
Bit 1: 1-dimensional coding, ITU-T Rec. T.4 (MH - Modified Huffman),
Bit 2: 2-dimensional coding, ITU-T Rec. T.4 (MR - Modified Read),
Bit 3: 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified MR),
Bit 4: ITU-T Rec. T.82 coding, using ITU-T Rec. T.85 (JBIG),
Bit 5: ITU-T Rec. T.81 (Baseline JPEG),
Bit 6: ITU-T Rec. T.82 coding, using ITU-T Rec. T.43 (JBIG color),
Bits 7-31: reserved for future use
Note: There is a limit of 32 compression types to identify standard
compression methods.
VersionYear(404) BYTE
Count: 4
The year of the standard specified by the FaxProfile field, given as
4 characters, e.g. '1997'; used in lossy and lossless color modes.
ModeNumber (405) BYTE
The mode of the standard specified by the FaxProfile field. A
value of 0 indicates Mode 1.0; used in Mixed Raster Content mode.
McIntyre, et. al. Standards Track [Page 17]
RFC 2301 File Format for Internet Fax March 1998
3. Minimal Black-and-White Fax Mode
This section defines the minimal black-and-white subset of TIFF for
facsimile. This subset is designated Profile S. All implementations
of TIFF for facsimile SHALL support the minimal subset.
Black-and-white mode is the binary fax application most users are
familiar with today. This mode is appropriate for black-and-white
text and line art. Black-and-white mode is divided into two levels of
capability. This section describes the minimal interchange set of
TIFF fields that must be supported by all implementations in order to
assure that some form of image, albeit black-and-white, can be
interchanged. This minimum interchange set is a strict subset of the
fields and values defined for the extended black-and-white mode
(TIFF-F or Profile F) in Section 4, which describes extensions to the
minimal interchange set of fields that provide a richer set of
black-and-white capabilities.
3.1. Overview
The minimal interchange portion of the black-and-white facsimile mode
supports 1-dimensional Modified Huffman (MH) compression, with the
original Group 3 fax resolutions, commonly called "standard" and
"fine."
To assure interchange, this mode uses the minimal set of fields, with
a minimal set of values. There are no recommended fields in this
mode. Further, the TIFF file is required to be "little endian," which
means that the byte order value in the TIFF header is "II". This mode
defines a required ordering for the pages in a fax document and for
the IFDs and image data of a page. It also requires that a single
strip contain the image data for each page; see Section 3.5. The
image data may contain RTC sequences, as specified in Section 3.4.
3.2. Required TIFF Fields
Besides the fields listed in Section 2.2.1, the minimal black-and-
white fax mode requires the following fields. The fields listed in
Section 2.2.1 and the fields and fax-specific values specified in
this sub- section must be supported by all implementations.
3.2.1 Baseline fields
BitsPerSample(258) = 1. SHORT
RequiredByTIFFBaseline
Binary data only.
Default = 1 (field may be omitted if this is the value)
McIntyre, et. al. Standards Track [Page 18]
RFC 2301 File Format for Internet Fax March 1998
Compression(259) = 3. SHORT
RequiredByTIFFBaseline
3 = 1- or 2- dimensional coding.
The value 3 is a TIFF extension value [TIFF]. The T4Options field
must be specified and its value specifies that the data is encoded
using the Modified Huffman (MH) encoding of [T.4].
FillOrder(266) = 2. SHORT
RequiredByTIFFBaseline
2 = Least Significant Bit first
NOTE: Baseline TIFF readers are only required to support FillOrder =
1, where the lowest numbered pixel is stored in the MSB of the byte.
However, because many devices, such as modems, transmit the LSB first
when converting the data to serial form, it is common for black-and-
white fax products to use the second FillOrder =2, where the lowest
numbered pixel is stored in the LSB. Therefore, this value is
specified in the minimal black-and-white mode.
ImageWidth(256) = 1728. SHORT or LONG
RequiredByTIFFBaseline
This mode only supports a page width of 1728 pixels. This width
corresponds to North American Letter and Legal and to ISO A4 size
pages.
No default, must be specified.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on, so may not be omitted for fax)
PhotometricInterpretation(262) = 0. SHORT
RequiredByTIFFBaseline
0 = pixel value 1 means black
No default, must be specified
ResolutionUnit(296) = 2. SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch.
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1. SHORT
RequiredByTIFFBaseline
The number of components per pixel; 1 for black-and-white
Default =1 (field may be omitted if this is the value)
XResolution(282) = 200, 204. RATIONAL
RequiredByTIFFBaseline
McIntyre, et. al. Standards Track [Page 19]
RFC 2301 File Format for Internet Fax March 1998
The horizontal resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are 200 and 204,
which may be treated as equivalent. See Section 2.2.2 for inch-
metric equivalency.
No default, must be specified
YResolution(283) = 98, 100, 196, 200. RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are 98, 100,
196 and 200; 98 and 100 may be treated as equivalent, and 196 and
200 may be treated as equivalent. See Section 2.2.2 for inch-metric
equivalency.
No default, must be specified
3.2.2 Extension fields
T4Options(292) = (Bit 0 = 0, Bit 1 = 0, Bit 2 = 0, 1) LONG
RequiredTIFFExtension (when Compression = 3)
Bit 0 = 0 indicates MH encoding.
Bit 1 must be 0
Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
aligned
Default is all bits are 0 (applies when EOLs are not byte aligned)
Note: The T4Options field is required when the Compression field has
a value of 3. Bit 0 of this field specifies the encoding used (MH
only in this mode) and Bit 2 indicates whether the EOL codes are
byte-aligned or not. If they are byte aligned, then fill bits have
been added as necessary so that the End of Line (EOL) codes always
end on byte boundaries. See Section 3.4 for details.
3.2.3. New Fields
None.
3.3. Recommended TIFF Fields
None.
3.4. End of Line (EOL) and Return to Control (RTC)
The handling of End of Line (EOL) codes and Return to Control (RTC)
sequences illustrate the differences between conventional fax, which
is bit and stream oriented, and TIFF, which is byte and file
oriented. Conventional fax, Baseline TIFF and TIFF extensions for fax
all handle EOLs and RTCs differently.
McIntyre, et. al. Standards Track [Page 20]
RFC 2301 File Format for Internet Fax March 1998
In conventional fax, an MH-compressed fax data stream for a page
consists of the following sequence:
EOL, compressed data (first line), EOL, compressed data, ... ,
EOL, compressed data (last line), RTC (6 consecutive EOL codes)
Baseline TIFF does not use EOL codes or Return to Control (RTC)
sequences for MH-compressed data. However, the TIFF extension field
T4Options used in this specification for MH compression (Compression
= 3) requires EOLs.
Furthermore, Bit 2 in the T4Options field indicates whether or not
the EOL codes are byte aligned. If Bit 2 = 1, indicating the EOL
codes are byte aligned, then fill bits have been added as necessary
before EOL codes so that an EOL code always ends on a byte boundary,
and the first bit of data following an EOL begins on a byte boundary.
Without fill bits, an EOL code may end in the middle of a byte. Byte
alignment relieves application software of the burden of bit-shifting
every byte while parsing scan lines for line-oriented image
manipulation (such as writing a TIFF file). Not all TIFF readers
historically used for fax are able to deal with non-byte aligned
data.
While TIFF extension requires EOL codes, TIFF in fax applications has
traditionally prohibited RTC sequences. Implementations that want
common processing and interfaces for fax data streams and Internet
fax files would prefer that the TIFF data include RTC sequences.
To reconcile these differences, RTCs are allowed in cases where EOL
codes are not byte aligned and no fill bits have been added to the
data. This corresponds to situations where the fax data is simply
inserted in a strip without being processed or interpreted. RTCs
should not occur in the data when EOLs have been byte aligned. This
is formally specified in the next sub-section.
3.4.1. RTC Exclusion
Implementations which wish to maintain strict conformance with TIFF
and compatibility with the historical use of TIFF for fax SHOULD NOT
include the RTC sequence when writing TIFF files. However,
implementations which need to support "transparency" of T.4-generated
image data MAY include RTCs when writing TIFF files if the flag
settings of the T4Options field are set for non-byte aligned data,
i.e. Bit 2 is 0. Implementors of TIFF readers should be aware that
there are some existing TIFF implementations for fax that include the
RTC sequence in MH image data. Therefore, minimal set readers MUST be
able to process files which do not include RTCs and SHOULD be able to
process files which do include RTCs.
McIntyre, et. al. Standards Track [Page 21]
RFC 2301 File Format for Internet Fax March 1998
3.5. File Structure
The TIFF header, described in Section 2.1.1, contains two bytes which
describe the byte order used within the file. For the minimal black-
and- white mode, these bytes SHALL have the value "II" (0x4949),
denoting that the bytes in the TIFF file are in LSByte-first order
(little- endian). The first or 0th IFD immediately follows the
header, so that offset to the first IFD is 8. The headers values are
shown in the following table:
+--------+-------------------+--------+-----------+
| Offset | Description | Value |
+--------+-------------------+--------+-----------+
| 0 | Byte Order | 0x4949 (II) |
+--------+-------------------+--------+-----------+
| 2 | Identifier | 42 decimal |
+--------+-------------------+--------+-----------+
| 4 | Offset of 0th IFD | 0x 0000 0008 |
+--------+-------------------+--------+-----------+
The minimal black-and-white mode SHALL order IFDs and image data
within a file as follows: 1) there SHALL be an IFD for each page in a
multi- page fax document; (2) the IFDs SHALL occur in the same order
in the file as the pages occur in the document; (3) the IFD SHALL
precede the image data to which it has offsets; (4) the image data
SHALL occur in the same order in the file as the pages occur in the
document; (5) the IFD, the value data and the image data it has
offsets to SHALL precede the next image IFD; and (6) the image data
for each page SHALL be contained within a single strip.
As a result of (6), the StripOffsets field will contain the pointer
to the image data. With two exceptions, the field entries in the IFD
contain the field values instead of offsets to field values located
outside the IFD. The two exceptions are the values for the
XResolution and YResolution fields, both of which are type RATIONAL
and require 2 4- byte numbers. These "long" field values SHALL be
placed immediately after the IFD which contains the offsets to them,
and before the image data pointed to by that IFD.
The effect of these requirements is that the IFD for the first page
SHALL come first in the file after the TIFF header, followed by the
long field values for XResolution and YResolution, followed by the
image data for the first page, then the IFD for second page, etc.
This is shown in the following figure. Each IFD is required to have a
PageNumber field, which has value 0 for the first page, 1 for the
second page, and so on.
McIntyre, et. al. Standards Track [Page 22]
RFC 2301 File Format for Internet Fax March 1998
+-----------------------+
| Header |------------+
+-----------------------+ | First IFD
| IFD (page 0) | <----------+ Offset
+---| |------------+
| | |--+ |
Value | +-----------------------+ | |
Offset +-->| Long Values | | |
+-----------------------| | Strip |
| Image Data (page 0) |<-+ Offset |
+-----------------------+ | Next IFD
| IFD (page 1) | <----------+ Offset
+---| |------------+
| | |--+ |
Value | +-----------------------+ | |
Offset +-->| Long Values | | |
+-----------------------| | Strip |
| Image Data (page 1) |<-+ Offset |
+-----------------------+ | Next IFD
| IFD (page 2) | <----------+ Offset
+-----------------------+
| : |
Using this file structure may reduce the memory requirements in
implementations. It is also provides some support for streaming, in
which a file can be processed as it is received and before the entire
file is received.
3.6 Minimal Black-and-white Mode Summary
The table below summarizes the TIFF fields that comprise the minimal
interchange set for black-and-white facsimile. The Baseline and
Extension fields and field values MUST be supported by all
implementations. For convenience in the table, certain fields which
have a value that is a sequence of flag bits are shown taking integer
values that correspond to the flags that are set. An implementation
should test the setting of the relevant flag bits individually,
however, to allow extensions to the sequence of flag bits to be
appropriately ignored. (See, for example, T4Options below.)
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1 |
+---------------------------+--------------------------------+
| Compression | 3: 1D Modified Huffman coding |
| | set T4Options = 0 or 4 |
+------------------------------------------------------------+
McIntyre, et. al. Standards Track [Page 23]
RFC 2301 File Format for Internet Fax March 1998
+---------------------------+--------------------------------+
| FillOrder | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageWidth | 1728 |
+---------------------------+--------------------------------+
| ImageLength | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType | 2: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| PageNumber | n,m: page number n followed by |
| | total page count m |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
+---------------------------+--------------------------------+
| ResolutionUnit | 2: inch |
+---------------------------+--------------------------------+
| RowsPerStrip | number of scanlines per strip |
| | = ImageLength, with one strip |
+---------------------------+--------------------------------+
| SamplesPerPixel | 1 |
+---------------------------+--------------------------------+
| StripByteCounts | number of bytes in TIFF strip |
+---------------------------+--------------------------------+
| StripOffsets | offset from beginning of |
| | file to single TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 204, 200 (pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98, 196, 100, 200 (pixels/inch)|
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| T4Options | 0: MH coding, EOLs not byte |
| | aligned |
| | 4: MH coding, EOLs byte aligned|
+---------------------------+--------------------------------+
4. Extended Black-and-White fax mode
This section defines the extended black-and-white mode or Profile F
of TIFF for facsimile. It provides a standard definition of what has
historically been known as TIFF Class F and now TIFF-F. In doing so,
it aligns this mode with current ITU-T Recommendations for black-
and-white fax and with existing industry practice. Implementations of
this profile include implementations of Profile S.
McIntyre, et. al. Standards Track [Page 24]
RFC 2301 File Format for Internet Fax March 1998
This section describes extensions to the minimal interchange set of
fields (Profile S) that provide a richer set of black-and-white
capabilities. The fields and values described in this section are a
superset of the fields and values defined for the minimal interchange
set in Section 3. In addition to the MH encoding, Modified READ (MR)
and Modified Modified READ (MMR) encoding as described in [T.4] and
[T.6] are supported.
Section 4.1 gives an overview of TIFF-F. Section 4.2 describes the
TIFF fields that SHALL be used in this mode. Section 4.3 describes
the fields that MAY be used in this mode. In the spirit of the
original TIFF-F specification, Sections 4.4 and 4.5 discuss technical
implementation issues and warnings. Section 4.6 gives an example use
of TIFF-F. Section 4.7 gives a summary of the required and
recommended fields and their values.
4.1 TIFF-F Overview
Though it has been in common usage for many years, TIFF-F has
previously never been documented in the form of a standard. An
informal TIFF-F document was originally created by a small group of
fax experts led by Joe Campbell. The existence of TIFF-F is noted in
[TIFF] but it is not defined. This document serves as the formal
definition of the F application of [TIFF] for Internet applications.
For ease of reference, the term TIFF-F will be used throughout this
document as a shorthand for the extended black-and-white mode or
profile of TIFF for facsimile.
Up until the TIFF 6.0 specification, TIFF supported various "Classes"
which defined the use of TIFF for various applications. Classes were
used to support specific applications. In this spirit, TIFF-F has
been known historically as "TIFF Class F". Previous informal TIFF-F
documents [TIFF-F0] used the "Class F" terminology. As of TIFF 6.0
[TIFF], the TIFF Class concept has been eliminated in favor of the
concept of Baseline TIFF. Therefore, this document updates the
definition of TIFF-F as the F profile of TIFF for facsimile, by using
Baseline TIFF as defined in [TIFF] as the starting point and then
adding the TIFF extensions to Baseline TIFF which apply for TIFF-F.
In almost all cases, the resulting definition of TIFF-F fields and
values remains consistent with those used historically in earlier
definitions of TIFF Class F. Where some of the values for fields
have been updated to provide more precise conformance with the ITU-T
[T.4] and [T.30] fax recommendations, these differences are noted.
McIntyre, et. al. Standards Track [Page 25]
RFC 2301 File Format for Internet Fax March 1998
4.2. Required TIFF Fields
This section lists the required fields and the values they must have
to be ITU-compatible. Besides the fields listed in Section 2.2.1, the
extended black-and-white fax mode SHALL use the following fields.
4.2.1. Baseline fields
BitsPerSample(258) = 1. SHORT
RequiredByTIFFBaseline
Binary data only.
Default = 1 (field may be omitted if this is the value)
Compression(259) = 3, 4. SHORT
RequiredByTIFFBaseline
3 = 1- or 2- dimensional coding, must have T4Options field This is
a TIFF Extension value [TIFF].
4 = 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified Modified
Read, must have T6Options field)) This is a TIFF Extension value.
Default = 1 (and is not applicable; field must be specified)
NOTE: Baseline TIFF permits use of value 2 for Modified Huffman
encoding, but data is presented in a form which does not use EOLs,
and so TIFF for facsimile uses Compression=3 instead. See Sections
4.4.4, 4.5.1 and 4.5.2 for more information on compression and
encoding.
FillOrder(266) = 1 , 2. SHORT
RequiredByTIFFBaseline
Profile F readers must be able to read data in both bit orders,
but the vast majority of facsimile products store data LSB
first, exactly as it appears on the telephone line.
1 = Most Significant Bit first.
2 = Least Significant Bit first
ImageWidth(256) SHORT or LONG
RequiredByTIFFBaseline
This mode supports the following fixed page widths: 1728, 2592, 3456
(corresponding to North American Letter and Legal, ISO A4 paper
sizes), 2048, 3072, 4096 (corresponding to ISO B4 paper size), and
2432, 3648, 4864 (corresponding to ISO A3 paper size).
No default; must be specified
NOTE: Historical TIFF-F did not include support for the following
widths related to higher resolutions: 2592, 3072, 3648, 3456, 4096
and 4864. Historical TIFF-F documents also included the following
values related to A5 and A6 widths: 816 and 1216. Per the most recent
McIntyre, et. al. Standards Track [Page 26]
RFC 2301 File Format for Internet Fax March 1998
version of [T.4], A5 and A6 documents are no longer supported in
Group 3 facsimile, so the related width values are now obsolete. See
section 4.5.2 for more information on inch/metric equivalencies and
other implementation details.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on, so may not be omitted for fax)
NOTE: Bit 1 is always set to 1 for TIFF-F, indicating a single page
of a multi-page image. The same bit settings are used when TIFF-F is
used for a one page fax image. See Section 4.4.3 for details on
multi-page files.
PhotometricInterpretation(262) = 0, 1. SHORT
RequiredByTIFFBaseline
0 = pixel value 1 means black, 1 = pixel value 1 means white.
This field allows notation of an inverted or negative image.
No default, must be specified
ResolutionUnit(296) = 2, 3. SHORT
RequiredByTIFFBaseline
The unit of measure for resolution. 2 = inch, 3 = centimeter; TIFF-F
has traditionally used inch-based measures.
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1. SHORT
RequiredByTIFFBaseline
1 = monochrome, bilevel in this case (see BitsPerSample)
Default =1 (field may be omitted if this is the value)
XResolution(282) = 200, 204, 300, 400, 408 RATIONAL
RequiredByTIFFBaseline
The horizontal resolution of the image is expressed in pixels per
resolution unit. In pixels/inch, the allowed values are: 200, 204,
300, 400, and 408. See Section 2.2.2 for inch-metric equivalency.
No default, must be specified
NOTE: The values of 200 and 408 have been added to the historical
TIFF-F values, for consistency with [T.30]. Some existing TIFF-F
implementations may also support values of 80 pixels/cm, which is
equivalent to 204 pixels per inch. See section 4.5.2 for information
on implementation details.
YResolution(283) = 98, 100, 196, 200, 300, 391, and 400 RATIONAL
RequiredByTIFFBaseline
The vertical resolution of the image is expressed in pixels per
McIntyre, et. al. Standards Track [Page 27]
RFC 2301 File Format for Internet Fax March 1998
resolution unit. In pixels/inch, the allowed values are: 98, 100,
196, 200, 300, 391, and 400 pixels/inch.
See Section 2.2.2 for inch-metric equivalency.
No default, must be specified
NOTE: The values of 100, 200, and 391 have been added to the
historical TIFF-F values, for consistency with [T.30]. Some existing
TIFF-F implementations may also support values of 77 and 38.5 (cm),
which are equivalent to 196 and 98 pixels per inch respectively. See
section 4.5.2 for more information on implementation details.
NOTE: Not all combinations of XResolution, YResolution and ImageWidth
are legal. The following table gives the legal combinations and
corresponding paper size [T.30].
+--------------+-----------------+---------------------------+
| XResolution x YResolution | ImageWidth |
+--------------+-----------------+---------+--------+--------+
| 200x100, 204x98 | | | |
| 200x200, 204x196 | 1728 | 2048 | 2432 |
| 204x391 | | | |
+--------------+-----------------+---------+--------+--------+
| 300 x 300 | 2592 | 3072 | 3648 |
+--------------+-----------------+---------+--------+--------+
| 408 x 391, 400 x 400 | 3456 | 4096 | 4864 |
+--------------+-----------------+---------+--------+--------+
|Letter,A4| B4 | A3 |
| Legal | | |
+---------+--------+--------+
| Paper Size |
+---------------------------+
4.2.2. Extension fields
T4Options(292) = (Bit 0 = 0 or 1, Bit 1 = 0, Bit 2 = 0 or 1) LONG
RequiredTIFFExtension (when Compression = 3)
T4Options was also known as Group3Options in a prior version of
[TIFF].
Bit 0 = 1 indicates MR encoding, = 0 indicates MH encoding.
Bit 1 must be 0
Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
aligned
Default is all bits are 0 (applies when MH encoding is used and EOLs
are not byte aligned EOLs) (See Section 3.2.2.)
The T4Options field is required when the Compression field has a
value of 3. This field specifies the encoding used (MH or MR) and
whether the EOL codes are byte-aligned or not. If they are byte
McIntyre, et. al. Standards Track [Page 28]
RFC 2301 File Format for Internet Fax March 1998
aligned, then fill bits have been added as necessary so that the End
of Line (EOL) codes always end on byte boundaries See Sections 3.4,
4.5.3 and 4.5.4 for details.
T6Options(293) = (Bit 0 = 0, Bit 1 = 0). LONG
RequiredTIFFExtension (when Compression = 4)
Used to indicate parameterization of 2D Modified Modified Read
compression. T6Options was also known as Group4Options in a prior
version of [TIFF].
Bit 0 must be 0.
Bit 1 = 0 indicates uncompressed data mode is not allowed; = 1
indicates uncompressed data is allowed (see [TIFF]).
Default is all bits 0. For FAX, the field must be present and have
the value 0. The use of uncompressed data where compression would
expand the data size is not allowed for FAX.
NOTE: MMR compressed data is two-dimensional and does not use EOLs.
Each MMR encoded image MUST include an "end-of-facsimile-block"
(EOFB) code at the end of each coded strip; see Section 4.5.6.
4.2.3. New fields
None.
4.3. Recommended TIFF fields
4.3.1. Baseline fields
See Section 2.2.3.
4.3.2. Extension fields
See Section 2.2.3.
4.3.3. New fields
Three new, optional fields, used in the original TIFF-F description
to describe page quality, are defined in this specification. The
information contained in these fields is usually obtained from
receiving facsimile hardware (if applicable). They SHOULD NOT be used
in writing TIFF-F files for facsimile image data that is error
corrected or otherwise guaranteed not to have coding errors. Some
applications need to understand exactly the error content of the
data. For example, a CAD program might wish to verify that a file
has a low error level before importing it into a high-accuracy
document. Because Group 3 facsimile devices do not necessarily
perform error correction on the image data, the quality of a received
page must be inferred from the pixel count of decoded scan lines. A
McIntyre, et. al. Standards Track [Page 29]
RFC 2301 File Format for Internet Fax March 1998
"good" scan line is defined as a line that, when decoded, contains
the correct number of pixels. Conversely, a "bad" scan line is
defined as a line that, when decoded, comprises an incorrect number
of pixels.
BadFaxLines(326) SHORT or LONG
The number of "bad" scan lines encountered by the facsimile device
during reception. A "bad" scanline is defined as a scanline that,
when decoded, comprises an incorrect number of pixels. Note that
PercentBad = (BadFaxLines/ImageLength) * 100
No default.
CleanFaxData(327) = 0, 1, 2. SHORT
Indicates if "bad" lines encountered during reception are stored in
the data, or if "bad" lines have been replaced by the receiver.
0 = No "bad" lines
1 = "bad" lines exist, but were regenerated by the receiver,
2 = "bad" lines exist, but have not been regenerated.
No default.
NOTE: Many facsimile devices do not actually output bad lines.
Instead, the previous good line is repeated in place of a bad line.
Although this substitution, known as line regeneration, results in a
visual improvement to the image, the data is nevertheless corrupted.
The CleanFaxData field describes the error content of the data. That
is, when the BadFaxLines and ImageLength fields indicate that the
facsimile device encountered lines with an incorrect number of pixels
during reception, the CleanFaxData field indicates whether these bad
lines are actually still in the data or if the receiving facsimile
device replaced them with regenerated lines.
ConsecutiveBadFaxLines(328) LONG or SHORT
Maximum number of consecutive "bad" scanlines received. The
BadFaxLines field indicates only the quantity of bad lines.
No Default.
NOTE: The BadFaxLines and ImageLength data indicate only the quantity
of bad lines. The ConsecutiveBadFaxLines field is an indicator of the
distribution of bad lines and may therefore be a better general
indicator of perceived image quality. See Section 4.4.5 for examples
of the use of these fields.
4.4. Technical Implementation Issues
4.4.1 Strips
In general, TIFF files divide an image into "strips," also known as
"bands." Each strip contains a few scanlines of the image. By using
McIntyre, et. al. Standards Track [Page 30]
RFC 2301 File Format for Internet Fax March 1998
strips, a TIFF reader need not load the entire image into memory,
thus enabling it to fetch and decompress small random portions of the
image as necessary.
The number of scanlines in a strip is described by the RowsPerStrip
value and the number of bytes in the strip after compression by the
StripByteCount value. The location in the TIFF file of each strip is
given by the StripOffsets values.
Strip size is application dependent. The recommended approach for
multi- page TIFF-F images is to represent each page as a single
strip. Existing TIFF-F usage is typically one strip per page in
multi-page TIFF-F files. See Sections 2.1.2 and 2.1.3.
4.4.2 Bit Order
The current TIFF specification [TIFF] does not require a Baseline
TIFF reader to support FillOrder=2, i.e. lowest numbered 1-bit pixel
in the least significant bit of a byte. It further recommends that
FillOrder=2 be used only in special purpose applications.
Facsimile data appears on the phone line in bit-reversed order
relative to its description in ITU-T Recommendation T.4. Therefore,
a wide majority of facsimile applications choose this natural order
for data in a file. Nevertheless, TIFF-F readers must be able to read
data in both bit orders and support FillOrder values of 1 and 2.
4.4.3. Multi-Page
Many existing applications already read TIFF-F-like files, but do not
support the multi-page field. Since a multi-page format greatly
simplifies file management in fax application software, TIFF-F
specifies multi-page documents (NewSubfileType = 2) as the standard
case.
It is recommended that applications export multiple page TIFF-F files
without manipulating fields and values. Historically, some TIFF-F
writers have attempted to produce individual single-page TIFF-F files
with modified NewSubFileType and PageNumber (page one-of-one) values
for export purposes. However, there is no easy way to link such
multiple single page files together into a logical multiple page
document, so that this practice is not recommended.
4.4.4. Compression
In Group 3 facsimile, there are three compression methods which had
been standardized as of 1994 and are in common use. The ITU-T T.4
Recommendation [T.4] defines a one-dimensional compression method
McIntyre, et. al. Standards Track [Page 31]
RFC 2301 File Format for Internet Fax March 1998
known as Modified Huffman (MH) and a two-dimensional method known as
Modified READ (MR) (READ is short for Relative Element Address
Designate). In 1984, a somewhat more efficient compression method
known as Modified Modified READ (MMR) was defined in the ITU-T T.6
Recommendation [T.6]. MMR was originally defined for use with Group 4
facsimile, so that this compression method has been commonly called
Group 4 compression. In 1991, the MMR method was approved for use in
Group 3 facsimile and has since been widely utilized.
TIFF-F supports these three compression methods. The most common
practice is the one-dimensional Modified Huffman (MH) compression
method. This is specified by setting the Compression field value to
3 and then setting bit 0 of the T4Options field to 0. Alternatively,
the two dimensional Modified READ (MR) method, which is much less
frequently used in historical TIFF-F implementations, may be selected
by setting bit 0 of the T4Options field to 1. The value of Bit 2 in
this field is determined by the use of fill bits.
Depending upon the application, the more efficient two-dimensional
Modified Modified Read (MMR)compression method from T.6 may be
selected by setting the Compression field value to 4 and then setting
the first two bits (and all unused bits) of the T6Options field to 0.
More information to aid the implementor in making a compression
selection is contained in Section 4.5.2.
Baseline TIFF also permits use of Compression=2 to specify Modified
Huffman compression, but the data does not use EOLs. As a result,
TIFF-F uses Compression=3 instead of Compression=2 to specify
Modified Huffman compression.
4.4.5. Example Use of Page-quality Fields
Here are examples for writing the CleanFaxData, BadFaxLines, and
ConsecutiveBadFaxLines fields:
1. Facsimile hardware does not provide page quality
information: MUST NOT write page-quality fields.
2. Facsimile hardware provides page quality information, but
reports no bad lines. Write only BadFaxLines = 0.
3. Facsimile hardware provides page quality information, and
reports bad lines. Write both BadFaxLines and
ConsecutiveBadFaxLines. Also write CleanFaxData = 1 or 2 if
the hardware's regeneration capability is known.
4. Source image data stream is error-corrected or otherwise
guaranteed to be error-free such as for a computer generated
file: SHOULD NOT write page-quality fields.
McIntyre, et. al. Standards Track [Page 32]
RFC 2301 File Format for Internet Fax March 1998
TIFF Writers SHOULD only generate these fields when the image has
been generated from a fax image data stream where error correction,
e.g. Group 3 Error Correction Mode, was not used.
4.4.6. Practical Guidelines for Writing and Reading Multi-Page TIFF-F
Files
Traditionally, historical TIFF-F has required readers and writers to
be able to handle multi-page TIFF-F files. Based on the experience
of various TIFF-F implementors, it has been seen that the
implementation of TIFF-F can be greatly simplified if certain
practical guidelines are followed when writing multi-page TIFF-F
files.
The structure for a multi-page TIFF-F file will include one IFD per
page of the document. In this case, this IFD will define the
attributes for a single page. A second simplifying guideline is that
the writer of TIFF-F files SHOULD present IFDs in the same order as
the actual sequence of pages. (The pages are numbered within TIFF-F
beginning with page 0 as the first page and then ascending (i.e. 0,
1, 2,...). However, any field values over 4 bytes will be stored
separately from the IFD. TIFF-F readers SHOULD expect IFDs to be
presented in page order, but be able to handle exceptions.
Per [TIFF], the exact placement of image data is not specified.
However, the strip offsets for each strip of image are defined from
within each IFD. Where possible, another simplifying guideline for
the writing of TIFF-F files is to specify that the image data for
each page of a multi-page document SHOULD be contained within a
single strip (i.e. one image strip per fax page). The use of a single
image strip per page is very useful for applications such as store
and forward messaging, where the file is usually prepared in advance
of the transmission, but other assumptions may apply for the size of
the image strip for applications which require the use of "streaming"
techniques (see section 4.4.7). In the event a different image strip
size guideline has been used (e.g. constant size for image strips
that may be less than the page size), this will immediately be
evident from the values/offsets of the fields that are related to
strips.
A third simplifying guideline is that each IFD SHOULD be placed in
the TIFF-F file structure at a point which precedes the image which
the IFD describes.
In addition, a fourth simplifying guideline for TIFF-F writers and
readers is to place the actual image data in a physical order within
the TIFF file structure which is consistent with the logical page
order. In practice, TIFF-F readers will need to use the strip
McIntyre, et. al. Standards Track [Page 33]
RFC 2301 File Format for Internet Fax March 1998
offsets to find the exact physical location of the image data,
whether or not it is presented in logical page order.
If the image data is stored in multiple strips, then the strips
SHOULD occur in the file in the same order that the data they contain
occurs in the facsimile transmission, starting at the top of the
page.
TIFF-F writers MAY make a fifth simplifying guideline, in which the
IFD, the value data and the image data to which the IFD has offsets
precede the next image IFD. However, this guideline has been relaxed
(writers MAY rather than SHOULD use it) compared to the other
guidelines given here to reflect past practices for TIFF-F.
In the case of the minimal mode, which is also the minimal subset of
Profile S, the SHOULD's and MAY's of these guidelines become SHALL's
(see Section 3.5).
So, a TIFF-F file which is structured using the guidelines of this
section will essentially be composed of a linked list of IFDs,
presented in ascending page order, which in turn each point to a
single page of image data (one strip per page), where the pages of
image data are also placed in a logical page order within the TIFF- F
file structure. (The pages of image data may themselves be stored in
a contiguous manner, at the option of the implementor).
4.4.7. Use of TIFF-F for Streaming Applications
TIFF-F has historically been used for handling fax image files in
applications such as store and forward messaging where the entire
size of the file is known in advance. While TIFF-F may also possibly
be used as a file format for cases such as streaming applications,
assumptions may be required that differ from those provided in this
section (e.g., the entire size and number of pages within the image
are not known in advance). As a result, a definition for the
streaming application of TIFF-F is beyond the scope of this document.
4.5. Implementation Warnings
4.5.1 Uncompressed data
TIFF-F requires the ability to read and write at least one-
dimensional T.4 Huffman ("compressed") data. Uncompressed data is
not allowed. This means that the "Uncompressed" bit in T4Options or
T6Options must be set to 0.
McIntyre, et. al. Standards Track [Page 34]
RFC 2301 File Format for Internet Fax March 1998
4.5.2. Encoding and Resolution
Since two-dimensional encoding is not required for Group 3
compatibility, some historic TIFF-F readers have not been able to
read such files. The minimum subset of TIFF-F REQUIRES support for
one dimensional (Modified Huffman) files, so this choice maximizes
portability. However, implementors seeking greater efficiency SHOULD
use T.6 MMR compression when writing TIFF-F files. Some TIFF-F
readers will also support two-dimensional Modified READ files.
Implementors that wish to have the maximum flexibility in reading
TIFF-F files should support all three of these compression methods
(MH, MR and MMR).
For the case of resolution, almost all facsimile products support
both standard (98 dpi) vertical resolution and "fine" (196 dpi)
resolution. Therefore, fine-resolution files are quite portable in
the real world.
In 1993, the ITU-T added support for higher resolutions in the T.30
recommendation including 200 x 200, 300 x 300, 400 x 400 in dots per
inch based units. At the same time, support was added for metric
dimensions which are equivalent to the following inch based
resolutions: 391v x 204h and 391v x 408h. Therefore, the full set of
inch-based equivalents of the new resolutions are supported in the
TIFF-F writer, since they may appear in some image data streams
received from Group 3 facsimile devices. However, many facsimile
terminals and older versions of TIFF-F readers are likely to not
support the use of these higher resolutions.
Per [T.4], it is permissible for applications to treat the following
XResolution values as being equivalent: <204,200> and <400,408>. In
a similar respect, the following YResolution values may also be
treated as being equivalent: <98, 100>, <196, 200>, and <391, 400>.
These equivalencies were allowed by [T.4] to permit conversions
between inch and metric based facsimile terminals.
In a similar respect, the optional support of metric based
resolutions in the TIFF-F reader (i.e. 77 x 38.5 cm) is included for
completeness, since they are used in some legacy TIFF-F applications,
but this use is not recommended for the creation of TIFF-F files by a
writer.
4.5.3. EOL byte-aligned
The historical convention for TIFF-F has been that all EOLs in
Modified Huffman or Modified READ data must be byte-aligned. However,
Baseline TIFF has permitted use of non-byte-aligned EOLs by default,
so that a large percentage of TIFF-F reader implementations support
McIntyre, et. al. Standards Track [Page 35]
RFC 2301 File Format for Internet Fax March 1998
both conventions. Therefore, the minimum subset of TIFF-F, or Profile
S, as defined in Section 3 includes support for both byte-aligned and
non- byte-aligned EOLs; see Section 3.2.2.
An EOL is said to be byte-aligned when Fill bits have been added as
necessary before EOL codes such that EOL always ends on a byte
boundary, thus ensuring an EOL-sequence of a one byte preceded by a
zero nibble: xxxx0000 00000001.
Modified Huffman encoding encodes bits, not bytes. This means that
the end-of-line token may end in the middle of a byte. In byte
alignment, extra zero bits (Fill) are added so that the first bit of
data following an EOL begins on a byte boundary. In effect, byte
alignment relieves application software of the burden of bit-
shifting every byte while parsing scan lines for line-oriented image
manipulation (such as writing a TIFF file).
For Modified READ encoding, each line is terminated by an EOL and a
one bit tag bit. Per [T.4], the value of the tag bit is 0 if the
next line contains two dimensional data and 1 if the next line is a
reference line. To maintain byte alignment, fill bits are added
before the EOL/tag bit sequence, so that the first bit of data
following an MR tag bit begins on a byte boundary.
4.5.4. EOL
As illustrated in FIGURE 1/T.4 in [T.4], facsimile documents encoded
with Modified Huffman begin with an EOL, which in TIFF-F may be byte-
aligned. The last line of the image is not terminated by an EOL. In
a similar respect, images encoded with Modified READ two-dimensional
encoding begin with an EOL, followed by a tag bit.
4.5.5. RTC Exclusion
Aside from EOLs, TIFF-F files have historically only contained image
data. This means that applications which wish to maintain strict
conformance with the rules in [TIFF] and compatibility with
historical TIFF-F, SHOULD NOT include the Return To Control sequence
(RTC) (consisting of 6 consecutive EOLs) when writing TIFF-F files.
However, applications which need to support "transparency" of [T.4]
image data MAY include RTCs if the flag settings of the T4Options
field are set for non-byte aligned MH or MR image data. Implementors
of TIFF readers should also be aware that there are some existing
TIFF-F implementations which include the RTC sequence in MH/MR image
data. Therefore, TIFF-F readers MUST be able to process files which
do not include RTCs and SHOULD be able to process files which do
include RTCs.
McIntyre, et. al. Standards Track [Page 36]
RFC 2301 File Format for Internet Fax March 1998
4.5.6 Use of EOFB for T.6 Compressed Images
TIFF-F pages which are encoded with the T.6 Modified Modified READ
compression method MUST include an "end-of-facsimile-block" (EOFB)
code at the end of each coded strip. Per [TIFF], the EOFB code is
followed by pad bits as needed to align on a byte boundary. TIFF
readers SHOULD ignore any bits other than pad bits beyond the EOFB.
4.6. Example Use of TIFF-F
The Profile F of TIFF (i.e. TIFF-F content) is a secondary component
of the VPIM Message, as defined in [VPIM2]. Voice messaging systems
can often handle fax store-and-forward capabilities in addition to
tradi- tional voice message store-and-forward functions. As a
result, TIFF-F fax messages can optionally be sent between compliant
VPIM systems, and may be rejected if the recipient system cannot deal
with fax.
Refer to the VPIM Specification for proper usage of this content.
4.7. Extended Black-and-white Fax Mode Summary
Recommended fields are shown with an asterisk *.
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the
Values column, then only the values suffixed with a double asterisk
are required of implementations.
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1** |
+---------------------------+--------------------------------+
| Compression | 3**: 1D Modified Huffman and |
| | 2D Modified Read coding |
| | 4: 2D Modified Modified Read |
| | coding |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
| FillOrder** | 1: most significant bit first |
| | 2: least significant bit first |
+------------------------------------------------------------+
McIntyre, et. al. Standards Track [Page 37]
RFC 2301 File Format for Internet Fax March 1998
+------------------------------------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth | 1728**, 2048, 2432, 2592, |
| | 3072, 3456, 3648, 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType | 2**: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
| ** | 1: pixel value 1 means white |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel | 1** |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release |
| | number of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number or bytes in TIFF |
| | strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning of |
| | file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 200, 204**, 300, 400, 408 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98**, 196**, 100, |
| | 200, 300, 391, 400 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
McIntyre, et. al. Standards Track [Page 38]
RFC 2301 File Format for Internet Fax March 1998
+---------------------------+--------------------------------+
| T4Options | 0**: required if Compression |
| | is Modified Huffman, EOLs are |
| | not byte aligned |
| | 1: required if Compression is |
| | 2D Modified Read, EOLs are |
| | not byte aligned |
| | 4**: required if Compression |
| | is Modified Huffman, EOLs are |
| | byte aligned |
+---------------------------+--------------------------------+
| T4Options (continued) | 5: required if Compression |
| | is 2D Modified Read, EOLs are |
| | byte aligned |
+---------------------------+--------------------------------+
| T6Options | 0: required if Compression is |
| | 2D Modified Modified Read |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of scanned |
| | document |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| BadFaxLines* | number of "bad" scanlines |
| | encountered during reception |
+---------------------------+--------------------------------+
| CleanFaxData* | 0: no "bad" lines |
| | 1: "bad" lines exist, but were |
| | regenerated by receiver |
| | 2: "bad" lines exist, but have |
| | not been regenerated |
+---------------------------+--------------------------------+
| ConsecutiveBadFaxLines* | Max number of consecutive |
| | "bad" lines received |
+---------------------------+--------------------------------+
5. Lossless JBIG Black-and-White Fax Mode
This section defines the lossless JBIG black-and-white mode or
Profile J of TIFF for facsimile. Implementations of this profile are
required to also implement Profile S.
McIntyre, et. al. Standards Track [Page 39]
RFC 2301 File Format for Internet Fax March 1998
The previous section described the extended interchange set of TIFF
fields for black-and-white fax, which provided support for the MH, MR
and MMR compression of black-and-white images. This section adds a
mode with JBIG compression capability.
5.1. Overview
This section describes a black-and-white mode that uses JBIG
compression. The ITU-T has approved the single-progression sequential
mode of JBIG [T.82] for Group 3 facsimile. JBIG coding offers
improved compression for halftoned originals. JBIG compression is
used in accordance with the application rules given in ITU-T Rec.
T.85 [T.85].
This mode is essentially the extended black-and-white mode with JBIG
compression used instead of MH, MR or MMR.
5.2. Required TIFF Fields
This section lists the required fields and the values they must have
to be ITU-compatible. Besides the fields listed in Section 2.2.1, the
extended black-and-white fax mode requires the following fields.
5.2.1. Baseline fields
The TIFF fields that SHALL be used in this mode are the same as those
described in Section 4.2.1 for the extended black-and-white mode,
with two exceptions: the following text replaces the text in Section
4.2.1 for the Compression and FillOrder fields.
Compression(259) = 9. SHORT
RequiredByTIFFBaseline
9 = ITU-T Rec. T.82 coding, applying ITU-T Rec. T.85 (JBIG). This is
a TIFF extension value.
Default = 1 (and is not applicable; field must be specified).
FillOrder(266) = 2. SHORT
RequiredByTIFFBaseline
2 = Pixels are arranged within a byte such that pixels with lower
column values are stored in the lower-order bits of the bytes, i.e.,
least significant bit first (LSB).
NOTE: The JBIG coding of black-and-white image data in Profile J
follows ITU-T Rec. T.85 [T.85], which specifies LSB first ordering
within a byte. Note that Baseline TIFF readers are only required to
support MSB first ordering or FillOrder = 1.
5.2.2. Extension fields
McIntyre, et. al. Standards Track [Page 40]
RFC 2301 File Format for Internet Fax March 1998
Same fields as those in Section 2.2.1.
5.2.3. New fields
None.
5.3. Recommended TIFF Fields
See Section 2.2.3 and 2.2.4.
5.4. Lossless JBIG Black-and-white Fax Mode Summary
Recommended fields are shown with an asterisk *.
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the
Values column, then only the values suffixed with a double asterisk
are required of implementations.
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 1** |
+---------------------------+--------------------------------+
| Compression | 9**: JBIG coding |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
| FillOrder** | 1: most significant bit first |
| | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth | 1728**, 2048, 2432, 2592, |
| | 3072, 3456, 3648, 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType** | 2: Bit 1 identifies single |
| | page of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+------------------------------------------------------------+
McIntyre, et. al. Standards Track [Page 41]
RFC 2301 File Format for Internet Fax March 1998
+---------------------------+--------------------------------+
| PhotometricInterpretation | 0: pixel value 1 means black |
| ** | 1: pixel value 1 means white |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel** | 1 |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release |
| | number of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number of bytes in TIFF |
| | strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning of |
| | file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 200, 204**, 300, 400, 408 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 98**, 196**, 100, |
| | 200, 300, 391, 400 |
| | (written in pixels/inch) |
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of document |
| | scanned |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| GlobalParametersIFD* | IFD: global parameters IFD |
+---------------------------+--------------------------------+
| ProfileType* | n: type of data stored in file |
+---------------------------+--------------------------------+
| FaxProfile* | n: ITU-compatible fax mode |
+---------------------------+--------------------------------+
| CodingMethods* | n: compression algorithms used |
| | in file |
+---------------------------+--------------------------------+
McIntyre, et. al. Standards Track [Page 42]
RFC 2301 File Format for Internet Fax March 1998
6. Base Color Fax Mode
6.1. Overview
This section defines the lossy color mode or Profile C of TIFF for
facsimile. Implementations of this profile are required to also
implement Profile S.
This is the base mode for color and grayscale facsimile, which means
that all applications that support color fax must support this mode.
The basic approach is the lossy JPEG compression [T.4, Annex E; T.81]
of L*a*b* color data [T.42]. Grayscale applications use the L*
lightness component; color applications use the L*, a* and b*
components.
This mode uses a new PhotometricInterpretation field value to
describe the L*a*b* encoding specified in [T.42]. This encoding
differs in two ways from the other L*a*b* encodings used in TIFF
[TIFF, TTN1]: it specifies a different default range for the a* and
b* components, based on a comprehensive evaluation of existing
hardcopy output, and it optionally allows selectable range for the
L*, a* and b* components.
6.2. Required TIFF Fields
This section lists the required fields, in addition to those given in
Section 2.2.1, and the values they must support to be compatible with
ITU-T Rec. T.42 and Annex E in ITU-T Rec. T.4.
6.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
This mode supports the following fixed page widths: 864, 1024, 1216,
1728, 2048, 2432, 2592, 3072, 3456, 3648, 4096, 4864.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on, so may not be omitted for fax)
BitsPerSample(258) = 8, 12. SHORT
Count = SamplesPerPixel
The base color fax mode requires 8 bits per sample, with 12 as an
option. 12 bits per sample is not baseline TIFF.
Compression(259) = 7. SHORT
Base color fax mode uses Baseline JPEG compression. Value 7
represents JPEG compression as specified in [TTN2].
McIntyre, et. al. Standards Track [Page 43]
RFC 2301 File Format for Internet Fax March 1998
FillOrder(266) = 1 , 2. SHORT
RequiredByTIFFBaseline
Profile C readers must be able to read data in both bit orders,
but the vast majority of facsimile products store data LSB
first, exactly as it appears on the telephone line.
1 = Most Significant Bit first.
2 = Least Significant Bit first
PhotometricInterpretation(262) = 10. SHORT
Base color fax mode requires pixel values to be stored using the CIE
L*a*b* encoding defined in ITU-T Rec. T.42. This encoding is
indicated by the PhotometricInterpretation value 10, referred to as
ITULAB. With this encoding, the minimum sample value is mapped to 0
and the maximum sample value is mapped to (2^n - 1), i.e. the
maximum value, where n is the BitsPerSample value. The conversion
from unsigned ITULAB-encoded samples values to signed CIE L*a*b*
values is determined by the Decode field; see Sec. 6.2.3
NOTE: PhotometricInterpretation values 8 and 9 specify encodings for
use with 8-bit-per-sample CIE L*a*b* [TIFF] and ICC L*a*b* [TTN1]
data, but they are fixed encodings, which use different minimum and
maximum samples than the T.42 default encoding. As currently defined,
they are not able to represent fax-encoded L*a*b* data.
ResolutionUnit(296) = 2, 3. SHORT
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1, 3. SHORT
1: L* component only, required in base color mode
3: L*, a*, b* components
Encoded according to PhotometricInterpretation field
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values are: 100, 200,
300, and 400. The base color fax mode requires the pixels to be
square, hence YResolution must equal XResolution. Base resolution is
200 pixels per inch and SHALL be supported by all implementations of
this mode. See Section 2.2.2 for inch-metric equivalency.
NOTE: Not all combinations of XResolution, YResolution and ImageWidth
are legal. The following table gives the legal combinations for inch-
based resolutions and the corresponding paper sizes [T.30].
McIntyre, et. al. Standards Track [Page 44]
RFC 2301 File Format for Internet Fax March 1998
+--------------------------------+---------------------------+
| XResolution x YResolution | ImageWidth |
+--------------------------------+---------------------------+
| 100 x 100 | 864 | 1024 | 1216 |
+--------------------------------+---------------------------+
| 200 x 200 | 1728 | 2048 | 2432 |
+--------------------------------+---------------------------+
| 300 x 300 | 2592 | 3072 | 3648 |
+--------------------------------+---------------------------+
| 400 x 400 | 3456 | 4096 | 4864 |
+--------------------------------+---------------------------+
|Letter,A4| B4 | A3 |
| Legal | | |
+---------------------------+
| Paper Size |
+---------------------------+
6.2.2 Extension Fields
The JPEG compression standard allows for the a*b* chroma components of
an image to be subsampled relative to the L* lightness component. The
extension fields ChromaSubSampling and ChromaPositioning define the
subsampling. They are the same as YCbCrSubSampling and YCbCrPositioning
in [TIFF], but have been renamed to reflect their applicability to other
color spaces.
ChromaSubSampling(530). SHORT
Count = 2
Specifies the subsampling factors for the chroma components of a
L*a*b* image. The two subfields of this field, ChromaSubsampleHoriz
and ChromaSubsampleVert, specify the horizontal and vertical
subsampling factors respectively.
SHORT 0: ChromaSubsampleHoriz = 1, 2.
1: equal numbers of lightness and chroma samples horizontally,
2: twice as many lightness samples as chroma samples horizontally,
SHORT 1: ChromaSubsampleVert = 1, 2.
1: equal numbers of lightness and chroma samples vertically,
2: twice as many lightness samples as chroma samples vertically,
The default value for ChromaSubSampling is (2,2), which is the
default for chroma subsampling in color fax [T.4, Annex E]. No
chroma subsampling, i.e. ChromaSubSampling = (1,1), is an option
for color fax
ChromaPositioning(531) = 1. SHORT
Specifies the spatial positioning of chroma components relative to
McIntyre, et. al. Standards Track [Page 45]
RFC 2301 File Format for Internet Fax March 1998
the lightness component.
1: centered,
A value of 1 means chrominance samples are spatially offset and
centered with respect to luminance samples. See the current TIFF
specification under YcbCr positioning for further information.
Default = 1, which is what ITU-T T.4, Annex E specifies.
6.2.3. New Fields
Decode(433). SRATIONAL
Count = 2 * SamplesPerPixel
Describes how to map image sample values into the range of values
appropriate for the current color space. In general, the values are
taken in pairs and specify the minimum and maximum output value for
each color component. For the base color fax mode, Decode has a
count of 6 values and maps the unsigned ITULAB-encoded sample values
(Lsample, asample, bsample) to signed L*a*b* values, as follows:.
L* = Decode[0] + Lsample x (Decode[1]-Decode[0])/(2^n -1)
a* = Decode[2] + asample x (Decode[3]-Decode[2])/(2^n -1)
b* = Decode[4] + bsample x (Decode[5]-Decode[4])/(2^n -1)
where Decode[0], Decode[2] and Decode[4] are the minimum values for
L*, a* and b*; Decode[1], Decode[3] and Decode[5] are the maximum
values for L*, a* and b*; and n is the BitsPerSample, either 8 or
12. For example, when n=8, L*=Decode[0] when Lsample=0 and
L*=Decode[1] when Lsample=255.
ITU-T Rec. T.42 specifies the ITULAB encoding in terms of a range
and offset for each component, which are related to the minimum and
maximum values as follows:
minimum = - (range x offset) / 2^n - 1
maximum = minimum + range
The Decode field default values depend on the color space. For the
ITULAB color space encoding, the default values correspond to the
base range and offset, as specified in ITU-T Rec. T.42 [T.42]. The
following table gives the base range and offset values for
BitsPerSample=8 and 12, and the corresponding default minimum and
maximum default values for the Decode field, calculated using the
equations above when PhotometricInterpetation=10.
McIntyre, et. al. Standards Track [Page 46]
RFC 2301 File Format for Internet Fax March 1998
+-----------------------------------------------+
| ITU-T Rec. T.42 | Decode |
+---------+-----------| base values | default values |
| BitsPer + Component +------------------+----------------------------+
| -Sample | | Range | Offset | Min | Max |
+---------+-----------+--------+---------+--------------+-------------+
| 8 | L* | 100 | 0 | 0 | 100 |
| +-----------+--------+---------+--------------+-------------+
| | a* | 170 | 128 | -21760/255 | 21590/255 |
| +-----------+--------+---------+--------------+-------------+
| | b* | 200 | 96 | -19200/255 | 31800/255 |
+---------+-----------+--------+---------+--------------+-------------+
| 12 | L* | 100 | 0 | 0 | 100 |
| +-----------+--------+---------+--------------+-------------+
| | a* | 170 | 2048 | -348160/4095 | 347990/4095 |
| +-----------+--------+---------+--------------+-------------+
| | b* | 200 | 1536 | -307200/4095 | 511800/4095 |
+---------+-----------+--------+---------+--------------+-------------+
For example, when PhotometricInterpretation=10 and BitsPerSample=8,
the default value for Decode is (0, 100, -21760/255, 21590/255,
-19200/255, 31800/255).
6.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
6.4 Base Color Fax Mode Summary
Recommended fields are shown with an asterisk *
Required fields or values are shown with a double asterisk **. If the
double asterisk is on the field name, then all the listed values are
required of implementations; if the double asterisks are in the
Values column, then only the values suffixed with a double asterisk
are required of implementations.
+---------------------------+--------------------------------+
| Baseline Fields | Values |
+---------------------------+--------------------------------+
| BitsPerSample | 8**: 8 bits per color sample |
| | 12: optional 12 bits/sample |
+---------------------------+--------------------------------+
| Compression** | 7: JPEG |
+---------------------------+--------------------------------+
| DateTime* | {ASCII}: date/time in 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+---------------------------+--------------------------------+
McIntyre, et. al. Standards Track [Page 47]
RFC 2301 File Format for Internet Fax March 1998
+------------------------------------------------------------+
| FillOrder** | 1: most significant bit first |
| | 2: least significant bit first |
+---------------------------+--------------------------------+
| ImageDescription* | {ASCII}: A string describing |
| | the contents of the image. |
+---------------------------+--------------------------------+
| ImageWidth | 864, 1024, 1216, 1728**, 2048 |
| | 2432, 2592, 3072, 3456, 3648 |
| | 4096, 4864 |
+---------------------------+--------------------------------+
| ImageLength** | n: total number of scanlines |
| | in image |
+---------------------------+--------------------------------+
| NewSubFileType** | 2: Bit 1 identifies single page|
| | of a multi-page document |
+---------------------------+--------------------------------+
| Orientation | 1**-8, Default 1 |
+---------------------------+--------------------------------+
| PhotometricInterpretation | 10**: ITULAB |
+---------------------------+--------------------------------+
| ResolutionUnit** | 2: inch |
| | 3: centimeter |
+---------------------------+--------------------------------+
| RowsPerStrip** | n: number of scanlines per |
| | TIFF strip |
+---------------------------+--------------------------------+
| SamplesPerPixel | 1**: L* (lightness) |
| | 3: LAB |
+---------------------------+--------------------------------+
| Software* | {ASCII}: name & release number |
| | of creator software |
+---------------------------+--------------------------------+
| StripByteCounts** | <n>: number or bytes in |
| | TIFF strip |
+---------------------------+--------------------------------+
| StripOffsets** | <n>: offset from beginning |
| | of file to each TIFF strip |
+---------------------------+--------------------------------+
| XResolution | 100, 200**, 300, 400 (written |
| | in pixels/inch) |
+---------------------------+--------------------------------+
| YResolution | 100, 200**, 300, 400 |
| | (must equal XResolution) |
+---------------------------+--------------------------------+
McIntyre, et. al. Standards Track [Page 48]
RFC 2301 File Format for Internet Fax March 1998
+---------------------------+--------------------------------+
| Extension Fields |
+---------------------------+--------------------------------+
| DocumentName* | {ASCII}: name of scanned |
| | document |
+---------------------------+--------------------------------+
| PageNumber** | n,m: page number followed by |
| | total page count |
+---------------------------+--------------------------------+
| ChromaSubSampling | (1,1), (2, 2)** |
| | (1, 1): equal numbers of |
| | lightness and chroma samples |
| | horizontally and vertically |
| | (2, 2): twice as many lightness|
| | samples as chroma samples |
| | horizontally and vertically |
+---------------------------+--------------------------------+
| ChromaPositioning | 1**: centered |
+---------------------------+--------------------------------+
| New Fields |
+---------------------------+--------------------------------+
| Decode** | minL, maxL, mina, maxa, minb, |
| | maxb: minimum and maximum |
| | values for L*a*b* |
+---------------------------+--------------------------------+
| GlobalParametersIFD* | IFD: IFD containing |
| | global parameters |
+---------------------------+--------------------------------+
| ProfileType* | n: type of data stored in |
| | TIFF file |
+---------------------------+--------------------------------+
| FaxProfile* | n: ITU-compatible fax mode |
+---------------------------+--------------------------------+
| CodingMethods* | n: compression algorithms |
| | used in file |
+---------------------------+--------------------------------+
| VersionYear* | byte sequence: year of ITU std |
+---------------------------+--------------------------------+
7. Lossless Color Mode
This section defines the lossless color mode or Profile L of TIFF for
facsimile. Implementations of this profile are required to also
implement Profiles S and C.
McIntyre, et. al. Standards Track [Page 49]
RFC 2301 File Format for Internet Fax March 1998
7.1. Overview
This mode, defined in [T.43], uses JBIG to losslessly code three
types of color and grayscale images: one bit per color CMY, CMYK and
RGB images; a palettized (i.e. mapped) color image; and continuous
tone color and grayscale images. The last two are multi-level and use
the L*a*b* encoding specified in [T.42].
7.1.1. Color Encoding
While under development, this mode was called T.Palette, as one of
its major additions was palette or mapped color images. Baseline TIFF
only allows RGB color maps, but ITU-T Rec. T.43 requires L*a*b* color
maps, using the encoding specified in ITU-T Rec. T.42. Palette color
images are expressed with indices (bits per sample) of 12 bits or
less, or optionally 13 to 16 bits, per [T.43].
Enabling T.43 color maps in TIFF requires the extension field
Indexed, defined in [TTN1], and the PhotometricInterpretation field
value 10, defined in Section 6.2.1. The following table shows the
corresponding PhotometricInterpretation, SamplesPerPixel,
BitsPerSample and Indexed field values for the different T.43 image
types.
+----------------------------------------------------------+
| Image Type |PhotometricIn| Samples | Bits Per | Indexed |
| |-terpretation| PerPixel | Sample | |
|------------+-------------+----------+----------+---------|
| RGB | 2=RGB | 3 | 1 | 0 |
+----------------------------------------------------------+
| CMY | 5=CMYK | 3 | 1 | 0 |
+------------+-------------+----------+----------+---------+
| CMYK | 5=CMYK | 4 | 1 | 0 |
+------------+-------------+----------+----------+---------+
| Palette | 10=ITULAB | 1 | n | 1 |
+------------+-------------+----------+----------+---------+
| Grayscale | 10=ITULAB | 1 | 8, 12 | 0 |
+------------+-------------+----------+----------+---------+
| Color | 10=ITULAB | 3 | 8, 12 | 0 |
+------------+-------------+----------+----------+---------+
7.1.2. JBIG Encoding
T.43 uses the single-progression sequential mode of JBIG, defined in
ITU-T Rec. T.82. To code multi-level images using JBIG, which is a
bi-level compression method, an image is resolved into a set of bit-
planes, and each bit-plane is then JBIG compressed. For continuous
tone color and grayscale images, Gray code conversion is used. The
McIntyre, et. al. Standards Track [Page 50]
RFC 2301 File Format for Internet Fax March 1998
Gray code conversion is part of the data stream encoding, and is
therefore invisible to TIFF.
7.2. Required TIFF Fields
This section lists the required fields, in addition to those in
Section 2.2.1, and the values they must have to be compatible with
ITU-T Rec. T.43.
7.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
Same page widths as the base color mode; see Section 6.2.1.
NewSubFileType(254) = (Bit 1=1). LONG
RequiredByTIFFforFAX
Bit 1 is 1 if the image is a single page of a multi-page document.
Default = 0 (no subfile bits on, so may not be omitted for fax)
BitsPerSample(258) = 1, 2-8, 9-16. SHORT
Count = SamplesPerPixel
RGB, CMY, CMYK: 1 bit per sample
Continuous tone (L*a*b*): 2-8 bits per sample, 9-12 bits optional
Palette color: 12 or fewer bits per sample, 13-16 bits optional
Note: More than 8 bits per sample is not baseline TIFF.
ColorMap(320). SHORT
Count = 3 * number of sample values
Lossless color fax mode supports palette-color (indexed) images
where the single component value is used as an index into a full
color lookup table stored in the ColorMap field. The sample value is
encoded using the number of bits given by the BitsPerSample field
value. However, per [T.43],the number of sample values may be less
than 2**BitsPerSample. The color lookup table is only required to
have as many entries as there are number of sample values. For
palette-color images in lossless color fax mode, the ITULAB encoding
with 8 or optionally 12 bits per color map value is supported. To
utilize a color map, the TIFF Indexed field must be present. TIFF
orders the color map values so that all the L* values come first,
followed by all the a* values and then all the b* values. Because
ITU-T Rec. T.43 specifies a "chunky" ordering with the L*a*b*
components of the first value, followed by those of the second
value, and so on, reproducing color map values from a fax data
stream in a TIFF file requires reordering values.
Compression(259) = 10. SHORT
10: ITU-T Rec. T.43 representation, using ITU-T Rec. T.82 (JBIG)
coding
McIntyre, et. al. Standards Track [Page 51]
RFC 2301 File Format for Internet Fax March 1998
FillOrder(266) = 1 , 2. SHORT
RequiredByTIFFBaseline
Profile F readers must be able to read data in both bit orders,
but the vast majority of facsimile products store data LSB
first, exactly as it appears on the telephone line.
1 = Most Significant Bit first.
2 = Least Significant Bit first
PhotometricInterpretation(262) = 2, 5, 10. SHORT
2: RGB
5: CMYK, including CMY
10: ITULAB
Image data may also be stored as palette color images, where pixel
values are represented by a single component that is an index into a
color map using the ITULAB encoding. This color map is specified by
the ColorMap field. To use palette color images, set the
PhotometricInterpretation to 10,SamplesPerPixel to 1, and Indexed to
1. The color map is stored in the ColorMap field. See Section 7.1.1
for further discussion on the color encoding.
ResolutionUnit(296) = 2, 3. SHORT
The unit of measure for resolution. 2 = inch, 3 = centimeter;
Default = 2 (field may be omitted if this is the value)
SamplesPerPixel(277) = 1, 3, 4. SHORT
1: Palette color image, or L*-only if Indexed = 0 and
PhotometricInterpretation is 10 (ITULAB).
3: RGB, or L*a*b*, or CMY if PhotometricInterpretation is 5 (CMYK).
4: CMYK.
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values are: 100, 200,
300, and 400. The lossless color fax mode requires the pixels to be
square, hence YResolution must equal XResolution. Base resolution is
200 pixels per inch. See Section 2.2.2 for inch-metric equivalency.
7.2.2. Extension Fields
Indexed(364) = 0, 1. SHORT
0: not a palette-color image
1: palette-color image
This field is used to indicate that each sample value is an index
into an array of color values specified in the ColorMap field.
Lossless color fax mode supports palette-color images with the
ITULAB encoding. The SamplesPerPixel value must be 1.
McIntyre, et. al. Standards Track [Page 52]
RFC 2301 File Format for Internet Fax March 1998
7.2.3. New Fields
Decode(433) SRATIONAL
Decode is used in connection with the ITULAB encoding of image data
and color map values; see Section 6.2.3.
7.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
7.4. Lossless Color Fax Mode Summary
Recommended fields are shown with an asterisk *.
+--------------------+--------------------------------------+
| Baseline Fields | Values |
+--------------------+--------------------------------------+
| BitsPerSample | 1: Binary RGB, CMY(K) |
| | 8: 8 bits per color sample |
| | 9-16: optional |
+--------------------+--------------------------------------+
| ColorMap | n: LAB color map |
+--------------------+--------------------------------------+
| Compression | 10: JBIG, per T.43 |
+--------------------+--------------------------------------+
| DateTime* | {ASCII}: date/time in the 24-hour |
| | format "YYYY:MM:DD HH:MM:SS" |
+--------------------+--------------------------------------+
| FillOrder** | 1: Most significant bit first |
| | 2: Least significant bit first |
+--------------------+--------------------------------------+
| ImageDescription* | {ASCII}: A string describing the |
| | contents of the image. |
+--------------------+--------------------------------------+
| ImageWidth | 864, 1024, 1216, 1728**, 2048, 2432, |
| | 2592, 3072, 3456, 3648, 4096, 4864 |
+--------------------+--------------------------------------+
| ImageLength** | n: total number of scanlines in image|
+--------------------+--------------------------------------+
| NewSubFileType | 2: Bit 1 identifies single page of a |
| | multi-page document |
+--------------------+--------------------------------------+
| Orientation | 1**-8, Default 1 |
+--------------------+--------------------------------------+
| PhotometricInter- | 2: RGB |
| pretation | 5: CMYK |
| | 10: ITULAB |
+--------------------+--------------------------------------+
McIntyre, et. al. Standards Track [Page 53]
RFC 2301 File Format for Internet Fax March 1998
+--------------------+--------------------------------------+
| ResolutionUnit | 2: inch |
| | 3: centimeter |
+--------------------+--------------------------------------+
| RowsPerStrip | n: number of scanlines per TIFF strip|
+--------------------+--------------------------------------+
| SamplesPerPixel | 1: L* (lightness) |
| | 3: LAB, RGB, CMY |
| | 4: CMYK |
+--------------------+--------------------------------------+
| Software* | {ASCII}: name & release number of |
| | creator software |
+--------------------+--------------------------------------+
| StripByteCounts | <n>: number or bytes in TIFF strip |
+--------------------+--------------------------------------+
| StripOffsets | <n>: offset from beginning of file to|
| | each TIFF strip |
+--------------------+--------------------------------------+
| XResolution | 100, 200, 300, 400 (written in |
| | pixels/inch) |
+--------------------+--------------------------------------+
| YResolution | equal to XResolution (pixels must be |
| | square) |
+--------------------+--------------------------------------+
| Extension Fields |
+--------------------+--------------------------------------+
| DocumentName* | {ASCII}: name of scanned document |
+--------------------+--------------------------------------+
| PageNumber | n,m: page number followed by total |
| | page count |
+--------------------+--------------------------------------+
| Indexed | 0: not a palette-color image |
| | 1: palette-color image |
+--------------------+--------------------------------------+
| New Fields |
+--------------------+--------------------------------------|
| Decode | minL, maxL, mina, maxa, minb, maxb: |
| |minimum and maximum values for L*a*b* |
+--------------------+--------------------------------------+
| GlobalParameters | IFD: global parameters IFD |
| IFD* | |
+-----------------------------------------------------------+
McIntyre, et. al. Standards Track [Page 54]
RFC 2301 File Format for Internet Fax March 1998
+--------------------+--------------------------------------+
| ProfileType* | n: type of data stored in TIFF file |
+--------------------+--------------------------------------+
| FaxProfile* | n: ITU-compatible fax mode |
+--------------------+--------------------------------------+
| CodingMethods* | n:compression algorithms used in |
| | file |
+--------------------+--------------------------------------+
| VersionYear* | byte sequence: year of ITU fax std |
+--------------------+--------------------------------------+
8. Mixed Raster Content Mode
This section defines the Mixed Raster Content mode or Profile M of
TIFF for facsimile. Implementations of this profile are required to
implement Profiles S and C, and may optionally implement Profiles F,
J and L.
8.1. Overview
Unlike previous fax modes, which use a single coding method and
spatial resolution for an entire fax page, the Mixed Raster Content
mode [T.44] enables different coding methods and resolutions within a
single page. For example, consider a page that contains black-and-
white text, which is best coded with MMR or JBIG, a color bar chart,
best coded with JBIG, and a scanned color image, best coded with
JPEG. Similarly, while spatial resolution of 400 pixels per inch may
be best for the black-and- white text, 200 pixel per inch is usually
sufficient for a color image.
Rather than applying one coding method and resolution to all
elements, MRC allows multiple coders and resolutions within a page.
By itself, MRC does not define any new coding methods or resolutions.
Instead it defines a 3-layer image model for structuring and
combining the scanned image data. The MRC 3-layer model has been
applied here using the TIFF format to yield a data structure which
differs from [T.44] though it applies the same coding methods, uses
the same compressed image data stream and is consistent with the TIFF
principle of a single IFD per image.
8.1.1. MRC 3-layer model
The 3 layers of the MRC model are Foreground and Background, which
are both multi-level, and Mask, which is bi-level. Each layer may
appear only once on a page and is coded independently of the other
two. In our earlier example, the black-and-white text could be in the
Mask layer, the color chart in the Foreground layer, and the color
image in the Background layer.
McIntyre, et. al. Standards Track [Page 55]
RFC 2301 File Format for Internet Fax March 1998
Each layer is an image and, when present, is represented by at least
one IFD in a TIFF file. This is consistent with TIFF, which provides
fields to define the attributes, such as resolution, image size, bits
per sample, etc., of a single image or layer. The distribution of
content among layers is determined by the writer, as is the choice of
coding method, color encoding and spatial resolution for a layer.
The final image is obtained by using the Mask layer to select pixels
from the other two layers. When the Mask layer pixel value is 1, the
corresponding pixel from the Foreground layer is selected; when it is
0, the corresponding pixel from the Background layer is selected.
Details are given in the Introduction of [T.44].
Not all pages, and not all parts of a page, require 3 layers. If
there is only one layer present, then that layer is the primary image
or IFD. If there is more than one layer, then the Mask must be one of
the layers, in which case it is the primary image and it must be page
size.
MRC allows a page to be split into strips, with a variable number of
scanlines in a strip. A strip can have 1, 2 or 3 layers. A single,
stripped layer may be stored as a single, stripped image in an IFD,
e.g., all strips associated with the Background layer may be treated
as a single image. Alternatively, each strip associated with a layer
may be stored as a separate image or IFD, e.g., the Background layer
can be composed of several images that are offset vertically with
respect to the page. In this case, there can be no overlap between
images associated with a single layer. According to [T.4] Annex G,
strips having more than 1 layer SHOULD NOT be more than 256 lines in
length unless the capability to receive longer strips has been
negotiated.
Furthermore, color fax also requires the spatial resolutions of
Background and Foreground images to be legal fax values that are also
integer factors of the Mask image resolution. For example, if the
Mask Layer resolution is 400 pixels per inch, then allowed
resolutions for the Foreground and Background layers are 100, 200 or
400 pixels per inch; if the Mask is at 300 pixels per inch, then
allowed values are 100 and 300. The Foreground and Background layer
resolutions can be independently set.
8.1.2. A TIFF Representation for the MRC 3-layer model
In the TIFF representation of the 3-layer MRC model, each page is
represented by a single IFD, called the Primary IFD, that represents
the Mask layer (unless the Foreground or Background is the single
layer present), and a set of child IFDs that are referenced through
the SubIFDs extension field [TTN1]. To distinguish MRC-specific
McIntyre, et. al. Standards Track [Page 56]
RFC 2301 File Format for Internet Fax March 1998
SubIFDs from other SubIFDs, the NewSubFileType field MUST have Bit 4
ON, indicating an MRC-related IFD. A new ImageLayer field is also
introduced that consists of two values that identify the layer
(Foreground, Background, or Mask) and the order within the layer
(first, second, ... image of the layer); see Section 8.2.3.
Because MRC allows strips with variable numbers of scanlines, a
reader MUST support StripRowCounts field because a writer may use it
in place of the RowsPerStrip field in this mode. The StripRowCounts
field allows each layer, with a variable number of scanlines in each
strip, to be represented by a single IFD, when the coding parameters
are the same for all strips in the layer. The MRC standard [T.44]
allows the Foreground and Background layers to have strips with
different coding parameters. In this case, a separate IFD is required
to represent the strips which use different coding parameters; see
text in next paragraph. In all cases, the Mask layer is required to
be represented by a single IFD and a single set of coding parameters.
The use of SubIFDs to store child IFDs is described in [TTN1]. An
example is shown graphically below. The Primary IFD associated with
page 1 (PrimaryIFD 0) points to page 2 (PrimaryIFD 1) with the
nextIFD offset. The Primary IFD, corresponding to the Mask layer
(ImageLayer=[2,1]), contains a SubIFDs field that points to a list of
child IFDs. The first child IFD represents one image of the
Background layer, i.e., ImageLayer=[1,1]. This child IFD points to
the second child IFD via the nextIFD offset. This child represents
the second Background layer image, ImageLayer=[1,2]. Finally, the
second child points to the third child, which corresponds to the
single Foreground layer image, ImageLayer=[3,1]. The next IFD offset
associated with this Foreground image is 0, indicating no more child
IFDs exist. Each primary IFD has the NewSubFileType set to 18,
indicating the IFD is MRC-specific (bit 4) and that it is a single
page of a multi-page document (bit 1). Each child IFD has the
NewSubFileType set to 16, indicating the IFD is MRC-specific. The 'V'
character should be read as a down-pointing arrow.
(nextIFD)
PRIMARY IFD 0 ------------> PRIMARY IFD 1--> ...
ImageLayer = [2,1]
NewSubFileType = 18
SubIFDs
|
V
Child IFD
ImageLayer = [1,1]
NewSubFileType = 16
|
|(nextIFD)
McIntyre, et. al. Standards Track [Page 57]
RFC 2301 File Format for Internet Fax March 1998
|
V
Child IFD
ImageLayer = [1,2]
NewSubFileType = 16
|
|(nextIFD)
|
V
Child IFD
ImageLayer = [3,1]
NewSubFileType = 16
|
|(nextIFD)
V
0
In the example above, the SubIFDs field of the Primary IFD points to
the first IFD in a list of child IFDs. TIFF allows the SubIFDs field
to point to an array of IFDs, each of which can be the first of a
list of IFDs. An MRC-enabled TIFF reader must scan all available
child IFDs to locate and identify IFDs associated with MRC layers.
In the case where the Background or Foreground layers are described
with multiple IFDs, the XPosition and YPosition TIFF fields specify
the offset to the upper-left corner of the IFD with respect to the
Mask layer; see Section 8.2.2. When there is only a single layer
(Mask, Foreground, or Background), it is stored as the Primary IFD.
8.2. Required TIFF Fields
This section describes the TIFF fields required, in addition to those
in Section 2.2.1, to represent MRC mode fax images. Since MRC mode
stores fax data as a collection of images corresponding to layers or
parts of layers, the coding methods, color encodings and spatial
resolutions used by previous modes apply to MRC. Therefore, the
descriptions here will typically reference the appropriate earlier
section. Fields and values specific to MRC mode are pointed out.
8.2.1. Baseline Fields
ImageWidth(256). SHORT or LONG
Same page widths as the base color mode; see Section 6.2.1.
In the MRC mode, the width of a Foreground or Background image in
the coded data stream may be less than the page width. In this case,
the image width in the coded data steam is used to interpret the
coded data, and the value of this field is used as the page width.
McIntyre, et. al. Standards Track [Page 58]
RFC 2301 File Format for Internet Fax March 1998
NewSubFileType(254) = 16, 18. LONG
For MRC fax mode, the NewSubFileType field has two bits that are
required.
Bit 1 indicates a single page of a multi-page document and must be
set for the Primary IFD;
Bit 4 indicates MRC imaging model as described in ITU-T
Recommendation T.44 [T.44], and must be set for Primary IFDs
and all MRC-specific child IFDs.
BitsPerSample(258) = 1, 2-8, 9-16 SHORT
Compression(259) = 3, 4, 7, 9, 10. SHORT
SamplesPerPixel(277) = 1, 3, 4. SHORT
FillOrder(266) = 1 , 2. SHORT
RequiredByTIFFBaseline
Profile F readers must be able to read data in both bit orders,
but the vast majority of facsimile products store data LSB
first, exactly as it appears on the telephone line.
1 = Most Significant Bit first.
2 = Least Significant Bit first
ResolutionUnit(296) = 2, 3. SHORT
PhotometricInterpretation(262) = 0, 1, 2, 5, 10. SHORT
For Mask layer, see Sections 4.2.1 and 5.2.1.
For Foreground and Background layers, see Sections 6.2.1 and 7.2.1.
ColorMap(320). SHORT
Count = 3 * (2**BitsPerSample)
Used when Foreground or Background layer is a palette-color image;
see Section 7.2.1.
XResolution(282) = 100, 200, 300, 400. RATIONAL
YResolution(283) = 100, 200, 300, 400. RATIONAL
The resolution of the image is expressed in pixels per resolution
unit. In pixels per inch, allowed XResolution values for all layers
are: 100, 200, 300, and 400. MRC color fax mode requires the pixels
to be square, hence YResolution must equal XResolution for all
layers. The resolution of Background and Foreground layers must each
be an integer factor of the Primary image, which is the Mask layer,
when it is present; see Section 8.4.
See Section 2.2.2 for inch-metric equivalency.
8.2.2. Extension Fields
ChromaSubSampling(530). SHORT
ChromaPositioning(531). SHORT
For Foreground and Background layers, see Section 6.2.2.
McIntyre, et. al. Standards Track [Page 59]
RFC 2301 File Format for Internet Fax March 1998
Indexed(346) = 0, 1. SHORT
For Foreground and Background layers: 1 indicates a palette-color
image, see Section 7.2.2.
T4Options(292) = 0, 1, 4, 5. SHORT
T6Options(293) = 0. SHORT
For Mask layer, see Section 4.2.2.
SubIFDs(330). IFD
Count = number of child IFDs
Each value is an offset from the beginning of the TIFF file to a
child IFD [TTN1].
XPosition(286). RATIONAL
YPosition(287). RATIONAL
Specifies the horizontal and vertical offsets of the top-left of the
IFD from the top-left of the Primary IFD in page resolution units.
For example, if the Primary IFD is at 400 pixels per inch, and a
foreground layer IFD is at 200 pixels per inch and located at pixel
coordinate (345, 678) with respect to the Primary IFD, the XPosition
value is 345/400 and the YPosition value is 678/400.
Color fax does not currently allow overlap of any component images
within a single layer.
Default values for XPosition and YPosition are 0.
8.2.3. New Fields
Decode(433). SRATIONAL
For Foreground and Background layers, see Section 6.2.3.
DefaultImageColor(434). SHORT
Count = SamplesPerPixel
In areas where no image data is available, a default color is needed
to specify the color value. If the StripByteCounts value for a strip
is 0, then the color for that strip must be defined by a default
image color.
The DefaultImageColor field uses the same encoding as the image
data, and its value is therefore interpreted using the
PhotometricInterpretation, SamplesPerPixel, BitsPerSample, and
Indexed fields. If the fax data stream requires a different
encoding, then transferring the default color value between a TIFF
file and fax data stream requires a color conversion.
For the Foreground layer image, the default value for the
DefaultImageColor field is black. For other cases, including the
Background layer image, the default value is white.
McIntyre, et. al. Standards Track [Page 60]
RFC 2301 File Format for Internet Fax March 1998
StripRowCounts(559). LONG
Count = number of strips
The number of scanlines stored in a strip. MRC allows each fax strip
to store a different number of scanlines. For strips with more than
one layer there is a maximum strip size of 256 scanlines or full
page size. The 256 maximum SHOULD be used unless the capability to
receive longer strips has been negotiated. This field replaces
RowsPerStrip for IFDs with variable-sized strips. Only one of the
two fields, StripRowCounts and RowsPerStrip, may be used in an IFD.
ImageLayer (34732). SHORT or LONG.
Count = 2
Image layers are defined such that layer 1 is the Background layer,
layer 3 is the Foreground layer, and layer 2 is the Mask layer,
which selects pixels from the Background and Foreground layers. The
ImageLayer tag contains two values, describing the layer to which
the image belongs and the order in which it is imaged.
ImageLayer[0] = 1, 2, 3.
1: Image is a Background image, i.e., the image that will appear
whenever the Mask contains a value of 0. Background images
typically contain low-resolution, continuous-tone imagery.
2: Image is the Mask layer. In MRC, if the Mask layer is present, it
must be the Primary IFD and be full page in extent (no gaps.)
3: Image is a Foreground image, i.e., the image that will appear
whenever the Mask contains a value of 1. The Foreground image
generally defines the color of text or lines, but may also
contain high-resolution imagery.
ImageLayer[1]:
1: first image to be imaged in this layer,
2: second image to be imaged in this layer,
3: ...
Value describing the image order. In MRC, this may be considered
the strip number. Since MRC mode currently does not allow overlap
between images within a layer, the order value does not have any
visual effect.
In MRC fax mode, it is possible that only a single layer is
transmitted. For example, if a page contains only a single
continuous-tone photograph, then only the Background layer may be
transmitted. In this case, the Background layer will be stored as the
Primary IFD. ImageLayer[0] will be 1 indicating Background;
ImageLayer[1] will be 1 since there can be no other IFDs associated
with that layer. No Mask layer will exist.
McIntyre, et. al. Standards Track [Page 61]
RFC 2301 File Format for Internet Fax March 1998
8.3. Recommended TIFF Fields
See Sections 2.2.3. and 2.2.4.
8.4. Rules and Requirements for Images
The MRC mode defines a fundamental set of rules for images in the 3-
layer representation.
1. If more than one layer exists, then the binary Mask layer SHALL be
present and be the primary image. The Mask layer SHALL support the
encoding defined in Section 3 and MAY support the encodings
defined in Sections 4 and 5. If only one layer exists, then the
image corresponding to that layer is the primary image.
2. When the binary Mask layer is the Primary IFD, the Primary IFD
defines and extends to the entire page boundary; all attached
model images cannot extend beyond the Primary image. Resolution
differences may cause some pixels to "hang over" the page
boundary, but no new pixels should exist completely beyond the
page extent. When the Foreground or Background layer is the
Primary IFD, the Primary IFD may not be page width.
3. The Background and Foreground images SHALL support the color
encoding defined in Section 6 and MAY support the color encoding
defined in Section 7. These images MAY optionally cover only a
portion of the strip or page.
4. Each Primary IFD and each MRC-specific SubIFD must have an
ImageLayer field to specify which layer the IFD belongs to, and
the imaging order of that IFD within the layer.
5. Each Primary IFD must have a NewSubFileType field value set to 18,
indicating a single page of a multi-page document (bit 1) and MRC
mode (bit 4).
6. Each MRC-specific child IFD must have a NewSubFileType field value
set to 16, indicating MRC mode (bit 4).
7. In MRC mode, each layer is transmitted as a sequence of strips. It
is possible that each strip of each layer can be stored as a
separate IFD. In this case, the SubIFDs structure pointed to by
the Primary IFD will contain several IFDs that have an ImageLayer
field with the layer identified as either Background (layer 1) or
Foreground (layer 3). There may be no overlap in the vertical
direction between IFDs associated with a single layer, although
McIntyre, et. al. Standards Track [Page 62]
RFC 2301 File Format for Internet Fax March 1998
there may be a gap from one of these images to the next. The TIFF
XPosition and YPosition fields are used to indicate the placement
of these images with respect to the primary image.
8. When the Mask image is present, the resolution of Background and
Foreground images must each be an integer factor of the Mask
image. For example, if the Mask image is 400 pixels/inch, then the
Background or Foreground image may be at 400 pixels/inch (400/1),
200 pixels/inch (400/2) or 100 pixels/inch (400/4).
8.5. MRC Fax Mode Summary
Recommended fields are shown with an asterisk *
+------------------+-----------------------------------------+
| Baseline Fields | Values |
|------------------|-----------------------------------------|
| BitsPerSample | 1: binary mask |
| | 8: 8 bits per color sample |
| | 9-16: optional 12 bits/sample |
+------------------+-----------------------------------------+
| ColorMap | n: LAB color map |
+------------------+-----------------------------------------+
| Compression | 3: Modified Huffman and Modified Read |
| | 4: Modified Modified Read |
| | 7: JPEG |
| | 9: JBIG, per T.85 |
| | 10: JBIG, per T.43 |
+------------------+-----------------------------------------+
| DateTime* | {ASCII): date/time in the 24-hour format|
| | "YYYY:MM:DD HH:MM:SS" |
+------------------+-----------------------------------------|
| FillOrder** | 1: Most significant bit first |
| | 2: Least significant bit first |
+------------------+-----------------------------------------|
| ImageDescription*| {ASCII}: A string describing the |
| | contents of the image. |
+------------------+-----------------------------------------+
| ImageWidth | 864, 1024, 1216, 1728**, 2048, 2432, |
| | 2592, 3072, 3456, 3648, 4096, 4864 |
+------------------+-----------------------------------------+
| ImageLength** | n: total number of scanlines in image |
+------------------+-----------------------------------------+
| NewSubFileType | 16, 18: |
| | Bit 1 indicates single page of a multi- |
| | page document on Primary IFD |
| | Bit 4 indicates MRC model |
+------------------+-----------------------------------------+
McIntyre, et. al. Standards Track [Page 63]
RFC 2301 File Format for Internet Fax March 1998
+------------------+-----------------------------------------+
| Orientation | 1**-8, Default 1 |
+------------------+-----------------------------------------+
| PhotometricInter | 0: WhiteIsZero |
| pretation | 1: BlackIsZero |
| | 2: RGB |
| | 5: CMYK |
| | 10: ITULAB |
+------------------+-----------------------------------------+
| ResolutionUnit | 2: inch |
| | 3: centimeter |
+------------------+-----------------------------------------+
| RowsPerStrip | n: number or scanlines per strip |
+------------------+-----------------------------------------+
| SamplesPerPixel | 1: L* (lightness) |
| | 3: RGB, LAB, CMY |
| | 4: CMYK |
+------------------+-----------------------------------------+
| Software* | {ASCII}: name & release number of |
| | creator software |
+------------------+-----------------------------------------+
| StripByteCounts | <n>: number or bytes in each strip |
+------------------+-----------------------------------------+
| StripOffsets | <n>: offset from beginning of file to |
| | each TIFF strip |
+------------------+-----------------------------------------|
| XResolution | 100, 200, 300, 400 (written in |
| | pixels/inch) |
+------------------+-----------------------------------------|
| YResolution | equal to XResolution (pixels must be |
| | square) |
+------------------+-----------------------------------------+
| Extension Fields |
+------------------+-----------------------------------------+
| T4Options | 0: required if Compression is Modified |
| | Huffman, EOLs not byte aligned |
| | 1: required if Compression 2D Modified |
| | Read, EOLs are not byte aligned |
| | 4: required if Compression Modified |
| | Huffman, EOLs byte aligned |
| | 5: required if Compression 2D Modified |
| | Read, EOLs are byte aligned |
+------------------+-----------------------------------------+
| T6Options | 0: required if Compression is 2D |
| | Modified Modified Read |
+------------------+-----------------------------------------+
McIntyre, et. al. Standards Track [Page 64]
RFC 2301 File Format for Internet Fax March 1998
+------------------+-----------------------------------------+
| DocumentName* | {ASCII}: name of scanned document |
+------------------+-----------------------------------------+
| PageNumber | n,m: page number followed by total page |
| | count |
+------------------+-----------------------------------------+
| ChromaSubSampling| (1,1), (2, 2)** |
| | (1, 1): equal numbers of lightness and |
| | chroma samples horizontally & vertically|
| | (2, 2): twice as many lightness samples |
| | as chroma horizontally and vertically |
+------------------+-----------------------------------------+
| ChromaPositioning| 1: centered |
+------------------+-----------------------------------------+
| Indexed | 0: not a palette-color image |
| | 1: palette-color image |
+------------------+-----------------------------------------+
| SubIFDs | <IFD>: byte offset to fg/bg IFDs |
+------------------+-----------------------------------------+
| XPosition | horizontal offset in primary IFD |
| | resolution units |
+------------------+-----------------------------------------+
| YPosition | vertical offset in primary IFD |
| | resolution units |
+------------------+-----------------------------------------+
| New Fields |
+------------------+-----------------------------------------+
| Decode | minL, maxL, mina, maxa, minb, maxb: |
| | minimum and maximum values for L*a*b* |
+------------------+-----------------------------------------+
| DefaultImageColor| <n>: background color |
+------------------+-----------------------------------------+
| StripRowCounts | <n>: number of scanlines in each strip |
+------------------+-----------------------------------------+
| ImageLayer | n, m: layer number, imaging sequence |
| | (e.g., strip number) |
+------------------+-----------------------------------------+
| GlobalParameters | IFD: global parameters IFD |
| IFD* | |
+------------------+-----------------------------------------+
| ProfileType* | n: type of data stored in TIFF file |
+------------------+-----------------------------------------+
| FaxProfile* | n: ITU-compatible fax mode |
+------------------+-----------------------------------------+
| CodingMethods* | n: compression algorithms used in file |
+------------------+-----------------------------------------+
| ModeNumber* | n: version of ITU fax standard |
+------------------+-----------------------------------------+
McIntyre, et. al. Standards Track [Page 65]
RFC 2301 File Format for Internet Fax March 1998
+------------------------------------------------------------+
| VersionYear* | byte sequence: year of ITU fax standard |
+------------------+-----------------------------------------+
9. MIME content-type image/tiff
[TIFF-REG] describes the registration of the MIME content-type
image/tiff to refer to TIFF encoded image data. When transported by
MIME, the TIFF content defined by this document must be encoded
within an image/tiff content type. In addition, an optional
"application" parameter is defined for image/tiff to identify a
particular application's subset of TIFF and TIFF extensions for the
encoded image data, if it is known. Typically, this would be used to
assist the recipient in dispatching a suitable rendering package to
handle the display or processing of the image file.
9.1 Refinement of MIME content-type image/tiff for Facsimile
Applications
Since this document defines facsimile specific profiles of TIFF, it
is useful to note an appropriate application parameter for the
image/tiff MIME content-type.
The two values of the image/tiff application parameter as defined for
facsimile are shown below, separated by a comma:
faxbw, faxcolor
The "faxbw" application parameter is suitable for use by applications
that can process one or more TIFF for facsimile profiles or subsets
used for the encoding of black and white facsimile data.
The "faxcolor" application parameter is suitable for use by
applications that can process one or more TIFF for facsimile profiles
or subsets that can be used for the encoding of black and white, AND
color facsimile data.
Since this document defines several profiles of TIFF for facsimile,
the following rules should be followed when setting the application
parameter value. For TIFF image data which is encoded for the
profiles of TIFF for Facsimile that support black-and-white image
data (Profiles S, F or J), applications which use one of these
profiles or a subset should set the value of the application
parameter to "faxbw". For TIFF image data which is encoded for the
defined profiles of TIFF for Facsimile that support color image data
(Profiles C, L or M), as well as black-and-white image data,
applications which use one of these profiles or a subset should set
the value of the application parameter to "faxcolor".
McIntyre, et. al. Standards Track [Page 66]
RFC 2301 File Format for Internet Fax March 1998
An example of the use of the image/tiff MIME Content-type with the
application parameter set with the value 'faxbw' follows:
Content-type: image/tiff; application=faxbw
In this example, use of this parameter value will enable applications
to identify the content as being within a profile or subset of TIFF
for Facsimile that is suitable for encoding black and white image
data, Before attempting to process the image data.
In a similar respect, an example of the image/tiff MIME Content-type
with the application parameter setting suitable for handling a color
subset or profile of TIFF for facsimile is shown below:
Content-type: image/tiff; application=faxcolor
10. Security Considerations
This document describes a file format for Internet fax, which is a
series of profiles of TIFF for facsimile. As such, it does not create
any security issues not already identified in [TIFF-REG], in its use
of fields as defined in [TIFF]. There are also new TIFF fields
defined within this specification, but they are of a purely
descriptive nature, so that no new security risks are incurred.
Further, the encoding specified in this document does not in any way
preclude the use of any Internet security protocol to encrypt,
authenticate, or non-repudiate TIFF-encoded facsimile messages.
11. References
[REQ] Bradner, S, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[T.4] ITU-T Recommendation T.4, Standardization of group 3 facsimile
apparatus for document transmission, October 1997
[T.6] ITU-T Recommendation T.6, Facsimile coding schemes and coding
control functions for group 4 facsimile apparatus, November 1988
[T.30] ITU-T Recommendation T.30 - Procedures for Document Facsimile
Transmission in the General Switched Telephone Network, June 1996
[T.42] ITU-T Recommendation T.42, Continuous-tone colour
representation method for facsimile, February 1996
McIntyre, et. al. Standards Track [Page 67]
RFC 2301 File Format for Internet Fax March 1998
[T.43] ITU-T Recommendation T.43, Colour and gray-scale image
representations using lossless coding scheme for facsimile, February
1997
[T.44] ITU-T Recommendation T.44, Mixed Raster Content (MRC), October
1997.
[T.81] ITU-T Recommendation T.81, Information technology - Digital
compression and coding of continuous-tone still images - Requirements
and guidelines, September 1992
[T.82] ITU-T Recommendation T.82, Information technology - Coded
representation of picture and audio information - Progressive bi-
level image compression, March 1995
[T.85] ITU-T Recommendation T.85, Application profile for
Recommendation T.82 - Progressive bi-level image compression (JBIG
coding scheme) for facsimile apparatus, August 1995
[TIFF] Tag Image File Format, Revision 6.0, Adobe Developers
Association, June 3, 1992,
ftp://ftp.adobe.com/pub/adobe/devrelations/
devtechnotes/pdffiles/tiff6.pdf
The TIFF 6.0 specification dated June 3, 1992 specification (c)
1986-1988, 1992 Adobe Systems Incorporated. All Rights Reserved.
[TIFF-FY] Parsons, G. and J. Rafferty, "Tag Image File Format (TIFF)
- F Profile for Facsimile", RFC 2306, March 1998.
[TIFF-F0] TIFF Class F specification, Apr 28, 1990,
ftp://ftp.faximum.com/pub/documents/tiff_f.txt
[TIFF-REG] Parsons, G., Rafferty J. and S. Zilles, "Tag Image File
Format (TIFF) - image/tiff MIME Sub-type Registration", RFC 2302,
March 1998.
[TTN1] Adobe PageMaker 6.0 TIFF Technical Notes, Sept. 14, 1995,
http://www.adobe.com/supportservice/devrelations/PDFS/TN/TIFFPM6.pdf
[TTN2] Draft TIFF Technical Note 2, Replacement TIFF/JPEG
specification, March 17, 1995,
ftp://ftp.sgi.com/graphics/tiff/TTN2.draft.txt
[VPIM2] Vaudreui,l G. and G. Parsons, "Voice Profile for Internet
Mail - version 2", work in progress, <draft-ema-vpim-06.txt>
The ITU-T Recommendations are available at http://www.itu.ch.
McIntyre, et. al. Standards Track [Page 68]
RFC 2301 File Format for Internet Fax March 1998
12. Authors' Addresses
Lloyd McIntyre Stephen Zilles
Xerox Corporation Adobe Systems Inc.
Mailstop PAHV-305 Mailstop W14
3400 Hillview Ave. 345 Park Avenue
Palo Alto, CA 94304 USA San Jose, CA 95110-2704, USA
Voice: +1-650-813-6762 Voice: +1-408-536-4766
Fax: +1-650-845-2340 Fax: +1-408-536-4042
Email: lmcintyre@adoc.xerox.com Email: szilles@adobe.com
Robert Buckley Dennis Venable
Xerox Corporation Xerox Corporation
Mailstop 0128-30E Mailstop 0128-27E
800 Phillips Road 800 Phillips Road
Webster, NY 14580, USA Webster, NY 14580, USA
Voice: +1-716-422-1282 Voice: +1-716-422-8009
Fax: +1-716-422-6117 Fax: +1-716-422-6117
Email: Rob_Buckley@wb.xerox.com Email: venable@wrc.xerox.com
Glenn S. Parsons James Rafferty
Northern Telecom Human Communications
P.O. Box 3511, Station C 12 Kevin Drive
Ottawa, ON K1Y 4H7, Canada Danbury, CT 06811-2901, USA
Phone: +1-613-763-7582 Phone: +1-203-746-4367
Fax: +1-613-763-2697 Fax: +1-203-746-4367
Email: Glenn.Parsons@Nortel.ca Email: Jrafferty@worldnet.att.net
McIntyre, et. al. Standards Track [Page 69]
RFC 2301 File Format for Internet Fax March 1998
Annex A: Summary of TIFF Fields for Internet Fax
This annex includes tables which list by mode the TIFF fields used in
the proposed fax file format. The fields are organized into 3
categories:
1) TIFF Baseline Fields
2) TIFF Extension Fields
3) New Fields.
The tables include the allowed values for each fax mode. Entries
other than explicit numbers are described by:
n - single number
n, m - 2 numbers
a, b, c - 3 numbers
r - rational number
<n> - array of numbers
<b> - byte sequence
{ASCII} - string
IFD - IFD byte offset
<IFD> - array of IFD byte offsets
A blank entry in the table indicates that the field is not used by
that particular fax mode.
Table A.1 TIFF Baseline Fields
+---------------------------------------------------------+
| Fax Mode/Profile |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| TIFF | | | | | | Content|
| Field | S | F | J | C | L | M |
+----------+---------+----------+--------+---------+--------+--------+
| BitsPer | 1 | 1 | 1 | 8, 12 | 1, 2-8 | 1, 2-8 |
| Sample | | | | | 9-16 | 9-16 |
+----------+---------+----------+--------+---------+--------+--------+
| ColorMap | | | | | <n> | <n> |
+----------+---------+----------+--------+---------+--------+--------+
| Compres- | 3 | 3, 4 | 9 | 7 | 10 | 3, 4, 7|
| sion | | | | | | 9,10 |
+----------+---------+----------+--------+---------+--------+--------+
| DateTime | | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
+----------+---------+----------+--------+---------+--------+--------+
| FillOrder| 2 | 1, 2 | 1, 2 | 1, 2 | 1, 2 | 1,2 |
+----------+---------+----------+--------+---------+--------+--------+
McIntyre, et. al. Standards Track [Page 70]
RFC 2301 File Format for Internet Fax March 1998
+----------+---------+----------+--------+---------+--------+--------+
| ImageDes-| | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
| cription | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Image- | n | n | n | n | n | n |
| Length | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Image- | 1728 | 1728, 2048, 2432 | 864, 1024, 1216, 1728, |
| Width | | 2592, 3072, 3456 | 2048, 2432, 2592, 3072, |
| | | 3648, 4096, 4864 | 3456, 3648, 4096, 4864 |
+----------+---------+----------+--------+---------+--------+--------+
| NewSub- | 2 | 2 | 2 | 2 | 2 | 16, 18 |
| FileType | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Orien- | 1 | 1-8 | 1-8 | 1-8 | 1-8 | 1-8 |
| tation | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Photo- | 0 | 0, 1 | 0, 1 | 10 | 2, 5, | 0, 1, |
| metric- | | | | | 10 | 2, 5, |
| Interp- | | | | | | 10 |
| retation | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Resolu- | 2 | 2, 3 | 2, 3 | 2, 3 | 2, 3 | 2, 3 |
| tionUnit | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| RowsPer- | n | n | n | n | n | n |
| Strip | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Samples- | 1 | 1 | 1 | 1, 3 | 1, 3, 4| 1, 3, 4|
| PerPixel | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Software | | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | n | <n> | <n> | <n> | <n> | <n> |
| Byte- | | | | | | |
| Counts | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | n | <n> | <n> | <n> | <n> | <n> |
| Offsets | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| XResolu- | 204 | 200, 204, 300 | 100, 200, 300, 400 |
| tion | 200 | 400, 408 | |
+----------+---------+----------+--------+---------+--------+--------+
| YResolu- | 98, 196 | 98, 196, 100, 200 | 100, 200, 300, 400 |
| tion | 100,200 | 300, 391, 400 | |
+----------+---------+----------+--------+---------+--------+--------+
McIntyre, et. al. Standards Track [Page 71]
RFC 2301 File Format for Internet Fax March 1998
Table A.2 TIFF Extension Fields
+---------------------------------------------------------+
| Fax Mode/Profile |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| TIFF | | | | | | Content|
| Field | S | F | J | C | L | M |
+----------+---------+----------+--------+---------+--------+--------+
| Chroma- | | | | 1 | | 1 |
| Position-| | | | | | |
| ing | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Chroma- | | | | <1, 1> | | <1, 1> |
| SubSampl-| | | | <2, 2> | | <2, 2> |
| ing | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Document-| | {ASCII} | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
| Name | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Indexed | | | | | 0,1 | 0,1 |
+----------+---------+----------+--------+---------+--------+--------+
| Page- | n, m | n, m | n, m | n, m | n, m | n, m |
| Number | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| SubIFDs | | | | | | <IFD> |
+----------+---------+----------+--------+---------+--------+--------+
| T4Options| 0, 4 | 0, 1, | | | | 0, 1, |
| | | 4, 5 | | | | 4, 5 |
+----------+---------+----------+--------+---------+--------+--------+
| T6Options| | 0 | | | | 0 |
+----------+---------+----------+--------+---------+--------+--------+
| XPosition| | | | | | r |
+----------+---------+----------+--------+---------+--------+--------+
| YPosition| | | | | | r |
+----------+---------+----------+--------+---------+--------+--------+
McIntyre, et. al. Standards Track [Page 72]
RFC 2301 File Format for Internet Fax March 1998
Table A.3 New Fields
+---------------------------------------------------------+
| Fax Mode/Profile |
+---------------------------------------------------------|
| Minimal | Extended | JBIG | Lossy |Lossless| Mixed |
+----------| B&W | B&W | B&W | Color | Color | Raster |
| TIFF | | | | | | Content|
| Field | S | F | J | C | L | M |
+----------+---------+----------+--------+---------+--------+--------+
| BadFax- | | n | | | | |
| Lines | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| CleanFax-| | 0, 1, 2 | | | | |
| Data | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Coding- | | | n | n | n | n |
| Method | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Consecu- | | n | | | | |
| tiveBad- | | | | | | |
| FaxLines | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Decode | | | | <r> | <r> | <r> |
+----------+---------+----------+--------+---------+--------+--------+
| Default- | | | | | | <n> |
|ImageColor| | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Fax- | | | n | n | n | n |
| Profile | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Global- | | IFD | IFD | IFD | IFD | IFD |
| Parame- | | | | | | |
| tersIFD | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Image- | | | | | | n, m |
| Layer | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Mode- | | | | | | n |
| Number | | | | | | |
+----------+---------+----------+--------+---------+--------+--------|
| Profile- | | | n | n | n | n |
| Type | | | | | | |
+--------------------------------------------------------------------+
McIntyre, et. al. Standards Track [Page 73]
RFC 2301 File Format for Internet Fax March 1998
+----------+---------+----------+--------+---------+--------+--------+
| Strip- | | | | | | <n> |
| RowCounts| | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
| Version- | | | | <b> |<b> | |
| Year | | | | | | |
+----------+---------+----------+--------+---------+--------+--------+
McIntyre, et. al. Standards Track [Page 74]
RFC 2301 File Format for Internet Fax March 1998
Annex B. IANA Registration for image/tiff Application Parameter
Values used for facsimile
To: IANA@isi.edu
Subject: Registration of new Application parameter values for
image/tiff
MIME media type name: image/tiff
Optional parameters: Application
New Value(s): faxbw, faxcolor
Description of Use:
faxbw - The "faxbw" application parameter is suitable for use by
applications that can process one or more TIFF for facsimile profiles
or subsets used for the encoding of black-and-white facsimile data.
The definition of the use of this value is contained in Section 9 of
this document (TIFFPLUS).
Faxcolor - The "faxcolor" application parameter is suitable for use
by applications that can process one or more TIFF for facsimile
profiles or subsets that can be used for the encoding of black and
white, AND color facsimile data. The definition of the use of this
value is contained in Section 9 of this document (TIFFPLUS).
McIntyre, et. al. Standards Track [Page 75]
RFC 2301 File Format for Internet Fax March 1998
Security Considerations:
Security considerations related to use of the TIFF subsets described
by the "faxbw" and "faxcolor" values of the Application parameter are
identified in Section 10 of this document (TIFFPLUS).
Persons & email addresses to contact for further information:
Glenn W. Parsons (Glenn.Parsons@Nortel.ca)
James Rafferty (Jrafferty@worldnet.att.net)
Stephen Zilles (szilles@adobe.com)
Change Controller: Stephen Zilles
INFORMATION TO THE SUBMITTER:
The accepted registrations will be listed in the "Assigned Numbers"
series of RFCs. The information in the registration form is freely
distributable.
McIntyre, et. al. Standards Track [Page 76]
RFC 2301 File Format for Internet Fax March 1998
Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
McIntyre, et. al. Standards Track [Page 77]