Images on the Web - Compression

Without compression, we would have no CD-ROMs, no DVDs and no one who wants to look at our pictures on the Web. Huge amounts of memory and storage space are required to transmit all of the information in a visual image into a a computer file. The more information--such as colors--the more storage space is required to hold the file in computer memory. This affects the storage space on your computer hard drive or server, on the web page and for the surfer who visits your page: consider how much memory you have, and how much time a surfer will spend waiting for the download, before adding multimedia elements (pictures, video, audio) to your site.

Compression, however, is one way to shrink computer files so that they are transmitted more quickly. There are two types of compression: lossless and lossy. For the former, the information in the file is chopped into smaller bits and when opened, it is reassembled into its original form without losing any of the original information. The latter type of compression, lossy, means that information is tossed away (not at random, however) shrinking the size of the bits retained. JPEG, a common file format for photographs, is a lossy compression technique, where redundant information is removed to shrink the size of the file.  

Depending on the type of the compression that you use, lossless or lossy, it is a good idea to keep a copy of the original, uncompressed file, just in case you want to make changes or notice that compression has removed elements from your file (or introduced new elements) that you had wanted to preserve (or are horrified that they have been added).

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Compression

Photographs

Digital Photography

Resources

Harris, Tom. How File Compression Works.