LASTTrue Color Vs. Indexed ColorNEXT

 

True Color
Color models with small bit-depths have gaps of missing colors that can't be represented within their coarse data structure. Models that can represent a large number of colors are known as "true color" or "continuous tone" because they can display images without obvious gaps. The most common true color model is 8-bit RGB, which can be used to represent 2^8 x 2^8 x 2^8, or 16,777,216, colors. When storing color information in a file, each pixel is assigned a byte of color information for each channel, so a 150 x 150 pixel true color image would require 67,500 bytes or about 66k in color data alone. Thus, uncompressed true color image file sizes tend to be quite large.
 
Specifying Color With Palettes

In order to reduce file sizes, an image with an index color palette uses a 1-dimensional array of color values called a palette, also called a color map, index map, color table, or look-up table (LUT). The color data in the file is stored as a series of small index values which is known as indirect, or pseudo-color storage. Instead of assigning a 3 byte value to each pixel, the index of the color table is used instead. Thus, an 8 bit paletted color file will be 1/3 the size of a true color file (although it can only display a limited 256 colors). Files can be made even smaller by chosing to use fewer colors than 256. Two colors would require only 1 bit per pixel, four 2/px, and eight 3/px, as seen in the example below.
True Color Example:
0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1 1 0 1 0 0 1 0 1 1 0 0 0 0 1 1 1 0 1 1 0 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1 1 0 1 1 0 1 0 0 1 0 0 0 0 0 0 1 1 0 1 1 1 0 1 0 1 0 0 1 1 1 1 0 1 0 1 1 1 0 0 0 0 1 0 1 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 0 0 1 0 1 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1
Index Color Example:
000 => 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1
001 => 1 0 1 0 0 1 0 1 1 0 0 0 0 1 1 1 0 1 1 0 1 0 0 0
010 => 1 0 1 1 0 1 0 0 1 0 0 0 0 0 0 1 1 0 1 1 1 0 1 0
011 => 1 0 0 1 1 1 1 0 1 0 1 1 1 0 0 0 0 1 0 1 0 0 0 0
100 => 1 1 0 1 0 0 0 1 0 1 1 1 0 0 0 1 1 0 0 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0 1 0 0 1 1 0 1 0 0 0 0 1 0 0 0 0 0
Which to Use?

(c) FreeFoto.com The choice has a dramatic impact on file size and image quality. Click on the image at right to cycle through a 2x magnified sample in true color and indexed to 256 and 32 colors. As a general rule of thumb, you'll want to use true color for photorealistic images and index color for simple graphics like charts & graphs.

Your choice of image file format also has an impact, since JPEG images are always true color, but PNGs can be any one of fifteen color formats including 8 & 16 bit RGB (true color) as well as 1, 2, 4 and 8 bit palettes (indexed).

Image Supplied by FreeFoto.com

 

LASTTable of ContentsFunction IndexNEXT