Image Compression (GIF/TIFF/PCX)

Abstract

Data communication increasingly involves the transmission of still and moving images. Compressing images into a standard form can give great savings in transmission times and storage lengths. Some of these forms are outlined in Table 4.1. The main parameters in a graphics file are:

• The picture resolution. This is defined by the number of pixels in the x-and y-directions.

• The number of colors per pixel. If N bits are used for the bit color then the total number of displayable colors will be 2^N. For example an 8-bit color field defines 256 colors, a 24-bit color field gives 2²⁴ or 16.7M colors. Many new computer systems allow for 32-bit color which gives over 4 billion colors.

• Palette size. Some systems reduce the number of bits used to display a color by reducing the number of displayable colors for a given palette size.