Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/12/84; site mit-hermes.ARPA Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!genrad!mit-eddie!mit-hermes!jpexg From: jpexg@mit-hermes.ARPA (John Purbrick) Newsgroups: net.micro.amiga Subject: Re: Interlaced monitor Message-ID: <2474@mit-hermes.ARPA> Date: Tue, 10-Sep-85 20:50:52 EDT Article-I.D.: mit-herm.2474 Posted: Tue Sep 10 20:50:52 1985 Date-Received: Thu, 12-Sep-85 11:46:53 EDT References: <6789@ucla-cs.ARPA> Organization: The MIT AI Lab, Cambridge, MA Lines: 43 > I can't figure out what an interlaced monitor is. > What will look better in the Amiga: 640x400, or > 640x200? Does it matter? > Adolfo This isn't net.video, but maybe that's why the question was asked. A conventional TV, and almost all computer monitors, use an interlaced scan. This means that 30 times a second the screen is drawn, first the odd- numbered lines and then the even ones. Thus each scan takes 1/60 second. The reason for this is that even though the information only has to be presented 30 times a second (easier for the memory) the flicker rate of the display will reflect the fact that two scans of the screen are being done. You may ask "Why not just write the screen all in one sweep 30 times a second?" but unfortunately 30 flashes a second is quite notice- able, hence the need to increase the flicker rate. Now, to the Amiga (and other displays with > 200 lines). 200 lines is a common resolution because what can be done is repeat each pixel on (say) line 69 in the same place on line 70. Then the pixel will be shown 60 times a second in one line or other, and the objectionable flicker is not seen; the eye doesn't readily notice that the pixel is actually jumping back and forth between lines. If you leave this system and go to a true 400 lines, you risk seeing the flicker of the individual pixels, an especially nasty bug if you draw horizontal or near-horizontal lines of only 1 pixel's width. One solution to the problem is to use a display with long-persistence phosphors, which continue to glow until the next time they are written. Unfortunately this plays havoc with moving objects (they leave a trail behind them) and the Amiga has extensive animation capability, so this isn't really a viable idea. It is certainly possible to get non-interlaced displays of 400, or many more, lines, which write at 60Hz and demand fast memories, but they cost a bundle and are essentially a specialty item. Since the computer and display have to agree on what the scanning procedure and bit rate are, the computer would have to be modified to use a true high-resolution monitor, even if you could afford one. If anyone knows how to get around this dilemma, I'd love to hear about it, as my ambition is to do CAD on the cheap. Oh yes, you can improve a display's apparent resolution by use of anti-aliasing, but that's another story. John Purbrick jpexg@mit-hermes.ARPA {...decvax!genrad! ...allegra!mit-vax!} mit-eddie!mit-hermes!jpexg