t measure 640-by-480 pixels. This is considerably smaller Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Chapter 5 than the NTSC standard of 768-by-484, or even the slightly different European PAL system. In modern systems, the user has great control over the resolution of the image, because he or she can vary the number of pixels on the screen. The pixels seen on the screen are simply memory representations of the information displayed. By selecting more pixels, and therefore better resolution, the graininess of the screen image is reduced. Some VGA adapters, for example, have resolutions as dense as 1024-by-768 pixels. The converse, of course, is also true. By selecting fewer pixels, and therefore increasing the graininess of the image, special effects can be created, such as "pixelization" or "tiling." Video Summary Let's review the factors and choices involved in creating video. The actual image is captured by a camera that is either analog or dig- ital. The resulting signal is then encoded on either analog or digital tape. If a VHS tape is to be the end result, it will be created directly from the original tape. If desktop video or CD-ROM video is the end result, then additional factors come into play. Because of the massive size of the original "file," it must be modified in some way to make it transportable to the new medium. It might be compressed, in which case a 200:1 reduction in size (or greater) could occur, with a resulting loss of quality (rain, for example, because it is a random event, tends to disappear in MPEG-compressed movies); it might be sampled less frequently, thus lowering the total number of frames, but causing the animation-like jerkiness that results from lower sampling rates; or, the screen size could be reduced, thus reducing the total number of pixels that need to be encoded. During the 