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To: Jay who wrote (47923)	2/16/1998 6:08:00 PM
From: Paul Engel	Read Replies (1) \| Respond to of 186894

Jay - Re: 320x200 pixels the result is far from satisfactory on playback." A "normal" TV picture is composed of an interlaced image of 256 scan lines representing "half" the image and another 256 scan lines representing the other "half" of the image. 30 times per second, both of these "half images" are displayed on a TV screen. One image of 256 scan lines occurs in 1/60 of a second, giving about 65 microseconds per line. The electron beam containing the image information is modulated at 3.58 MHz, which allows about 233 equivalent "pixels" per line. Thus, a TV image is only 256 x 2 x 233 = 119,296 "equivalent" pixels - far fewer than a simple VGA display (640 x 480 = 307,200} Perhaps more importantly, the color "depth" of each pixel is such that it can display one color out of 16 million possibilities - which gives rise to the "allusion" of a sharp picture. In reality, this wide spectrum of colors allows for a near-continuous distribution in colors. This permits a smooth gradation in color from one feature to another in the single image. Sharp, abrupt and jaggy transitions are avoided in this manner. The 16,000,000+ colors requires 3 bytes (2^8 = 256) for each color, one byte each for red, green and blue. Now, consider the data density that must be delivered EVERY SECOND to emulate a real TV signal. 3 Bytes/Pixel x 119,296 pixels/screen*60 screens/second = 21.5 Million bytes/second! Accordingly, to see a "full screen" video of only 512 x 233 pixels, 21.5 million BYTES of data must be delivered EVERY second to simulate a broadcast signal. A one minute flick then requires 1.3 Gigabytes of data. All this assumes no data compression or use of such "data saving" techniques. So what you have is an enormous amount of information per screen image that must be "digitized" and stored, then re-displayed to give you the digital version of your home video. Therein lies the problems you have referred to. Enormous data storage and a tremendous delivery rate of that data from memory/disk to a Video display chip are serious system constraints on quality and quantity of "digitized video". Many compromises are made in current systems, as you have encountered, that degrade the quality of the image unless postage-stamp-sized images are used to "compress" the data. Paul