June 30, 2004
Types of Images for the Web
Computer image files can be very large. For example, a three-inch square image suitable for printing in a book can be up to three megabytes in size. Fortunately, there are ways to compress image files. This is important because most people access Web pages over a modem line, and modems are relatively slow when downloading large image files. For example, a three-megabyte file would take about 14 minutes to download over a 28.8K modem connection. If the same file were compressed, it might take just one or two seconds to download. 
Two Popular Compressed File Formats
There are two file formats that are most popular for displaying images on the Web: 
* GIF (Graphic Exchange Format)?The GIF format compresses a file by examining the image for consistent patterns and then rewriting the digital image to a shorthand based on those repeated patterns, reducing the number of colors used to display the picture. The GIF format can compress images by about 4:1.
* JPEG (Joint Photographic Experts Group)?JPEG format compresses a file by tossing out subtle color differences in the image that human eyes are less likely to recognize. Depending on the level of image quality you require, JPEG can accomplish compression ratios between 10:1 and 100:1

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Assessment 12.2		Lesson 12: Web Integration—Posting an Online Resume


Word 2003		Page 1