ding a 3:1 compression ratio. GIF's LZW compression scheme doesn't work well on photographs, yielding maximum compression levels of 5:1-and some- times far less. Because the human eye is more sensitive to luminance variations than it is to variations in color, JPEG compresses color data more than it does brightness data. Generally speaking, a gray-scale image that is 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 JPEG encoded only achieves a 10 to 25 percent reduction of a full-color JPEG file of similar quality. The uncompressed gray-scale image com- prises eight bits per pixel, or roughly a third of the color data. As a result, the compression ratio is much lower. Tag Image File Format (TIFF) TIFF is a tag-based image format designed to promote the interoper- ability of digital images. The format came into being in 1986 when Aldus Corporation, working with leading scanner vendors, created a standard file format for images to be used in desktop publishing applications. The first version of the specification was published in July 1986; more cur- rent versions are released regularly by Adobe and are available at their Web sites. The format that defines a file specifies both the structure of the file and its content. TIFF content consists of a series of definitions of indi- vidual fields. The structure, on the other hand, describes how to actually find the fields. These "pointers" are called tags. TIFF provides a general-purpose format that is compatible with a variety of scanners and image-processing applications. It is device- independent and is acceptable to most operating systems, including Win- dows, Macintosh, and UNIX. The standard has been integrated into most scanner manufacturers' software and desktop publishing applications. Adobe continues to enhance TIFF within publishing applications and maintains backward co