Chapter 18: Working with Graphics

How Do Computers Handle Images?

For a computer to display, edit, or otherwise work with an image, that image has to be represented as data and stored in a file. In general, this is done by transforming the image into an array of small rectangles called pixels. Each pixel has only one color. If the pixels are small enough, the human eye doesn't notice this transformation, but if the rectangular components are visible the image is said to be pixelated. A number can represent the color of each pixel, and the list of all these numbers is then turned into a file.

A file created in this way is very large, but fortunately much of this information is redundant. (Very often, for example, pixels next to each other have similar colors.) This fact allows an image file to be compressed into a smaller file from which a computer can recreate the original image file when needed. This compression can be done in a variety of ways, depending on whether the purpose of the compression is to create the smallest possible file, to represent the image most accurately, or to perform the compression as quickly as possible. Each compression method produces a different image file format. The most popular image formats are .bmp, .pcx, .gif, .jpg, and .tif.