Aucbvax.1371 fa.human-nets utzoo!duke!mhtsa!eagle!ucbvax!DERWAY@MIT-ML Tue May 19 19:22:55 1981 HUMAN-NETS Digest V3 #101 HUMAN-NETS AM Digest Sunday, 17 May 1981 Volume 3 : Issue 101 Today's Topics: FYI - Call for Proposals for NCC '82, Computers and the Handicapped - Color Blindness, Query Replies - 3D Displays & Voice Grade Line Bandwidth ---------------------------------------------------------------------- Date: 14 May 1981 (Thursday) 1714-EDT From: MORGAN at WHARTON-10 (Howard Morgan) Subject: NCC '82 For those of you who read human-nets, please submit proposals for sessions, or papers, directly to MORGAN@WHARTON. As technical program chairman, I will examine submissions and proposals, and route them to appropriate program committee members. Any of you who would like to help with NCC in other ways, please let me know via message. Howard Morgan ------------------------------ Date: 13 May 1981 1155-EDT From: GEOF at MIT-XX Subject: Re: HUMAN-NETS Digest V3 #98 RE: Colorblindness. It is unfortunate that we use red and green for no/yes stop/go signals, since red/green confusion is the most common of all. The problem, however, is well known, especially to designers of road signs. For example, most traffic lights are mounted vertically, with red at the top. If you can see the socket (a problem at night), you can tell the color from the context. One set of horizontal lights I saw uses a diamond for yellow, a square for red, and a circle for green. An added clue is that there are always two red lights lit. Similarly, in Quebec there are two sets of road- signs: those that mean you must do X and those that mean you may NOT do X (i.e., no left turn can be "no left turn" or "straight and right only"). The signs were originally identical, except that the Must's were circled in green and the Don't's in red. The colorblindness problem presented itself, and was solved by introducing a red diagonal into the Don't signs. If a colorblind person can't understand a public computer display, the fault is clearly with the designer of the software. There are no end of additional clues which may be devised. Of course, it is not always evident just what the clues mean (who says that a square means red and a circle green). But for PUBLIC displays, people who need the clues can find out for themselves rather quickly, given that the clues are simple and consistent. In a private display, like the VLSI plots mentioned, the problem is more difficult, and it is not clear that it need be solved in every case (sorry to all you color blind out there). For example, I don't think there is a way around fancy plotting problems, other than choosing pencils of radically different luminences (you might also try flourescent and metallic colors). The real solution is to use a color graphics printer, where the lines can be textured. Xerox software uses texture to display similar plots on a black and white dover. ------------------------------ Date: 7 May 1981 1206-EDT From: SWG at MIT-XX Subject: stereo display By coincidence, I just read "Going to the Roundies" in the March Scientific American's "Science and the Citizen". Excerpts: Investigators at the Cinema and Photographic Research Institute [C.P.R.I.] in Moscow are at work on a holographic motion-picture system for public theaters. In 1976 the group exhibited a 45-second holographic movie in which a young woman holding a bouquet of flowers in front of her face seems to walk out of the screen toward the audience. Each viewer, by moving his head horizontally or vertically, could look around the bouquet and see the woman's face. The effect was startling, although the registration of the image from frame to frame was not perfect and the color was unrealistic (the image was yellow). The movie and the way it was made are described by Tung H. Jeong of Lake Forest College in \Optical Spectra/. In the years since the 45-second movie was shown the techniques of holographic cinematography have improved considerably. The recent developments are discussed by two members of the Moscow group, Victor G. Komar and O. I. Ioshin, in \SMPTE Journal/, a publication of the Society of Motion Picture and Television Engineers. . . . The theoretical and technological difficulties in extending holography to motion pictures are substantial. The [C.P.R.I.] is one of only a few institutions where the work has been attempted. Surprisingly, the most challenging problems may lie not in making holographic motion pictures but in projecting them to a large audience. The projection of the hologram onto an ordinary movie screen would destroy the reconstructive property of the image. It is necessary for the observer to intercept not a projection of the light rays emerging from the hologram but the rays themselves. One hypothetical method of presentation, explained by Jeong, would employ a mirror rather than a diffusely reflective screen as the projection surface. For example, the mirror might be an elliptical one with two foci. The viewer would sit at one focus and the holographic image would be formed at the other focus. [I assume the image degrades gradually as the viewer moves away from the focus.] The drawback to this method is that it would work only for an audience of one. For a larger audience the screen would have to be equivalent to a superposition of as many mirrors as there are viewers, with the image at a common focus and each seat at the second focus of one of the mirrors. It is impossible, however, to combine mirrors in this way. The investigators in Moscow, according to Jeong, overcame the problem by employing as the screen a specially constructed hologram that has the same multiple-focusing property as superposed mirrors would have. The hologram is made by exposing a photographic plate the size of the screen [!] to beams diverging from each seat in the theater and from the point where the image will be formed. When light rays from the projector impinge on the holographic screen, they come to a focus at each seat. The movie of the woman and the bouquet was shown with a screen that could accommodate an audience of four. The investigators plan to construct a seven-foot-wide holographic screen for an audience of between 200 and 400 viewers. [No doubt the size of the screen limits not the size of the image but rather its brightness, resolution, etc.] ------------------------------ Date: 12 May 1981 1055-MDT From: Spencer W. Thomas Subject: Stereopsis A comment on displays which attempt to simulate 3-D by presenting a different image to each eye (so called 'stereo pairs'). A fair portion of the population cannot see any depth in these images (something astounding on the order of 20-30%). Back in the early days of graphics, Ivan Sutherland was working on a stereo display, and was having much difficulty getting it to work. Finally, he asked a colleague, who said 'But this is great!'. Sutherland went out and got his eyes tested and discovered that he couldn't see depth in stereo pairs. (Allegedly a true story.) We once came up with 7 cues to depth in normal viewing of the 'real' world: 1. Stereopsis 2. Motion parallax 3. Perspective 4. Occlusion of further objects by nearer objects 5. Color saturation (as things get further away, they tend towards less saturated colors due to atmospheric effects) 6. Size cues (i.e. you know how big a person should be, so if heesh looks too small, heesh must be far away. 7. Focus. I'm sure that if you think about it, you can come up with some more. =S ------------------------------ Date: 11 MAY 1981 2308-PDT From: CAULKINS at USC-ECL Subject: voice grade lines + 9600 baud We recently leased a line from the phone company spec'd to be DC continuity between the two connected points. We hung some short distance modems on the line, but were unable to push more than 4800 baud over the line (we too hoped for 9600). When we checked with the telco wizards they said that there were loading coils in the line, and we were lucky to get 4800. To get the loading coils removed would cost a mere $1500. We are resigned to running at 4800. Dave C ------------------------------ Date: 12 May 1981 01:39-EDT From: Charles Frankston Subject: baud vs. bps and line driver performance issues A baud is a signal transition. As someone else pointed out, a signal transition can very well be used to encode more than one bit of information (quadrature modulation and other techniques). Therefore 9600 baud may not necessarily equal 9600 bits per second. Its as simple as that. However, the computer industry constantly misuses the word baud. It would have been much clearer for your terminal manufacturer to say your terminal ran at 9600 bps. Your line driver not being able to run 10 miles at 9600 bps is hardly surprising. First thing that comes to mind is that the line you are leasing from the phone company may not have DC continuity (ie. it is not just a set of wires). It used to be hard to obtain a "metallic" circuit from the phone company, but most seem to offer it now. There are probably equalizers (capacitors) etc. on the line. Even without that, there are not that many line drivers that are rated for that speed at 10 miles (in fact I can't think of a single one offhand). There ARE some short haul modems that can probably make it, (The difference between a short haul modem and a line driver is that a modem maintains continuous carrier on the line. The problem a line driver will run into at high speed is that the signal transitions having to charge a line up from the idle state on every signal transition first have to charge the capacitor represented by a metallic pair of any substantial length.) but they are generally more expensive ($800 or so vs. $200 or less) than line drivers. Other obvious factors affecting performance would be the gauge of the wire and how well twisted it was. Is the readership really interested in these low level telecommincations issues? I seem to remember a huge number of issues back recommending McNamara's book "Technical Aspects of Data Communications" available from Digital Press (yes, that publisher is Digital Equipment Corporation). ------------------------------ Date: 12 May 1981 1119-PDT Subject: Leased line and line drivers. From: the tty of Geoffrey S. Goodfellow Having been outfitted with a 9600 baud leased line to my house for several months now, perhaps I can offer some help. Firstly, you MUST make sure the line(s) you have [it takes two pair, i.e. 4 wires] are Non-loaded and have DC continuity. You order the lines from your local TPC mentioning this and Bell specification #43401. Secondly, I do not know of any regular/standard line-drivers that will drive 9600 baud over 4 miles. However, Prentice offers a line-driver (the one I am currently using for my hookup) called the ALD-XR (for eXtended Range) that'll handle 9600 baud up to 6 miles. Their regular ALD only goes 4 miles for 9600 baud. I found all this out when Prentice sent me the regular ALD's by mistake first and I couldn't go any faster than 2400 baud (my home Datamedia only goes 110, 300, 1200, 2400 or 9600), and sent them back and got the ALD-XR's. I get a few hits on the line every now and then, with an occasional tilda appearing in my output, but it only happens every couple of days. Here's Prentice's table: Miles with Non-Loaded 26-AWG Cable Baud ALD ALD-XR 1200 10 15 2400 8 12 4800 6 9 7200 5 7.5 9600 4 6 >From the looks of this, I'm not surprised you can't go over 2400 baud (providing you have an ALD-XR or equalvalient). Guess you'll just have to move in closer or spring for expen$ive and big modems if you still want 9600. ------------------------------ End of HUMAN-NETS Digest ************************ ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.