Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.micro.amiga Subject: Re: Interlaced monitor Message-ID: <5973@utzoo.UUCP> Date: Mon, 16-Sep-85 19:37:17 EDT Article-I.D.: utzoo.5973 Posted: Mon Sep 16 19:37:17 1985 Date-Received: Mon, 16-Sep-85 19:37:17 EDT References: <6789@ucla-cs.ARPA> <204@cirl.UUCP>, <30637@lanl.ARPA> Organization: U of Toronto Zoology Lines: 19 The reason why interlace is a more serious compromise for a computer display than for normal video is that normal video doesn't usually have a lot of one-pixel detail in it. The picture on any interlaced display is made up of pixels flashing at 30 Hz. If a whole area of pixels are (roughly) the same color, then the eye will average out the alternating 30-Hz flashing into a 60-Hz flash frequency for the whole area. When color changes drastically from one pixel to the next, this averaging can't happen. TV pictures generally are composed of substantial areas of continuous color. Computer displays often have one-pixel-wide lines and characters with one-pixel-wide strokes. Consider a pattern of well-separated white one-pixel dots on a black background. If the dots are all in even-numbered scan lines, then in the first 60th of a second all the dots are refreshed, and in the second 60th of a second nothing happens. So the net refresh rate is 30 Hz, and the interlace is useless. This is an extreme case, mind you. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry