User Guide

Academic Courseware: Chapter 1

Joyce Ryan

for all the colors. But what does it mean when you are working with a

32-bit image? What are those other 8 bits for, if they’re not needed to

display the RGB colors? They are used for transparency. Certain file

formats support “alpha channels.” Having an 8-bit alpha channel means

that you can have 256 levels of transparency in your image. Color

resolution, or bit depth, affects not only the file size (fewer colors means

fewer bits), but also the smoothness of the color gradations in an image.

This image has excellent color resolution.

Here is the same image using only 60 colors (it has decreased color depth). Look closely

at the green boat and the clouds; notice how the colors are simplified. This effect is called

“posterization.”

There is an important

difference between displayable and

definable color. If you have 24 bits of

color, you can define over 16.7 million

colors. If your display is set for 1024 x

768, you only have 786,432 pixels,

so you can only display 786,432 colors

out of a possible 16.7 million.