Image Processing Basics - Digital Signal Processing: Fundamentals and Applications - page 687

14.1.3 8-Bit Color Images
The 8-bit color image is also a popular image format. Its pixel value is a color index that points to
a color lookup table containing RGB components. We call this a color indexed image , and its format
is shown in Figure 14.6 . As an example in the figure, the color indexed image has a pixel index
value of 5, which is the index for the entry of the color table, called the color map . At location 5 in
the color table, there are three color components with RGB values of 66, 132, and 34, respectively.
Each color component is encoded in 8 bits. There are only 256 different colors in the image. A
640 480 8-bit color image requires 307.2 kilobytes for data storage and 3 256 ¼ 768 bytes for
color map storage. The 8-bit color image for the cruise ship shown in Figure 14.3 is displayed in
Figure 14.7 .

R G B

Index

0
5 01000010 10000100 00100010

255

0 n 0 n

0 0

Pixel value

5

R = 66
G=1 3 2
B=34

Index value

m

m

FIGURE 14.6

The 8-bit color indexed image format.

FIGURE 14.7
The 8-bit color indexed image.