June 30, 2004

Hyperlink Test

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)¾The
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)¾JPEG
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