Here are a few lines about the "BIFF" file format, the format used in
the XITE system. XITE - X-based Image processing Tools and Environment
- is a free system from dept. of informatics, university of Oslo,
Norway.  The format is quite simple, and I see no point in describing
it in detail, but I would like to mention a few features that we are
satisfied with.

First of all, the format is only 3D (unfortunately, it should be
N-dim.).  It defines an image to be a sequence of 2D bands. Every band
may have its own size and pixel type, which even allows the pyramide
representation to be used. There are also separate parameters for
positioning and magnification of each band. Any amount of ascii text
may also be stored on the same file.  The whole structure is read from
file in one call, and represented in one data structure, something
like (in C):

  IMAGE i;
  i = read_image(filename);

Then the image i may be asked for number of bands:

  fprintf("Number of bands: %d\n", nbands(i));

It may also be indexed:

  fprintf("Pixel value: %d\n", i[band][y][x]);

The bands may be handled separately:

  BAND b;
  b = i[1];  /* pointer to first band */
  fprintf("Size of band: %d x %d\n", xsize(b), ysize(b));
  fprintf("Pixel value: %d\n", b[y][x]);

The data structures represent pixel values as well as corresponding
information, thus only one parameter must be transferred to functions.

The format defines a number of pixel types, but most functions are
only implemented for the byte pixel type. The function can test the
arriving band to see if it has correct pixel type, something like:

  if (pixeltype(b) != unsigned_byte) ...

A final feature is the sub-band mechanism. A sub-band is a _pointer_
to a rectangular subset of a band. When transferred to a function, the
function does not have to distingwish between "normal" bands, and
sub-bands. To negate some rectangular part of a band b1:

  BAND b2;
  b2 = sub-band(b1, x1, x2, y1, y2); /* define the rectangular subset of b1 */
  negate(b2, b2);   /* two parameters because in general different  
                       input and output are used, in this case
                       identical parameters are allowed.
                       If b1 is now displayed, we see that the subset
                       is negated. */ 



To conclude: the file format allows some important flexibility
(different size and pixel type in each band), and it is very easy to
write programs using the format, as a "memory-format" is, defined and
the neccessary functions are written.

I will be glad to answer any questions.

Sincerely,
Tor Lonnestad
Dept. of Informatics
University of Oslo
Norway
e-mail: tor@ifi.uio.no