alculates an average Figure 2-20 My son, Steve 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. Protocols Protocols Figure 2-21 Steve's chin, enlarged to show color ranges among pixels value for each group of pixels. Additional steps in the process further reduce the pixel count, resulting in a dramatic reduction in the total number of pixels required to represent the original image-hence the term "lossy." To restore the image, the reverse process is invoked. JPEG is a 24-bit color scheme that yields high degrees of color fidelity. Unfortunately, many users do not have access to 24-bit color monitors, which means that a JPEG-encoded image will not display the image cor- rectly. To display a full-color image, the host computer must analyze the file, choose an appropriate set of representative colors from a color "chart," and map the image into the new color domain. This process is known as color quantization. The speed and image quality of a JPEG viewer used on a lower qual- ity machine is largely determined by its quantization algorithm. If the algorithm is complex and well designed, the user will see minimal impact on the image from the quantization process. If the encoder is infe- rior, however, the result will be equally inferior. Of course, there are ways around this. GIF image are already quan- tized to 256 or fewer colors (GIF doesn't allow more than 256 color palette entries.) GIF has the advantage that the creator of the image cal- culates the degree of color quantization SO that viewers do not have to. For this reason, GIF viewers are typically faster than JPEG viewers. Of course, this also limits the user to whatever constraints the GIF viewer places on the image. If the creator of the image quantized the original image to a level that cannot be achieved by a receiving device, the image will have to be further quantized, resulting i