The number of bits per screen pixel determines the display's screen bit depth . The screen bit depth determines the screen color resolution , which is how many distinct colors the display can produce.
Some systems use the extra bit to increase the number of levels of green that can be displayed.
Choosing a Screen Bit Depth Depending on your system, you may be able to choose the screen bit depth you want to use. In general, 24-bit display mode produces the best results. There are only 32 shades of gray available. If you are working primarily with grayscale images, you may get better display results using 8-bit display mode, which provides up to 256 shades of gray. For information about reducing the number of colors used by an image, see Reducing the Number of Colors in an Image .