Bit-Depth Number of Colors Type
1 2 monochrome
2 4 CGA
4 16 EGA
8 256 VGA
16 65,536 High Color, XGA
24 16,777,216 True Color, SVGA
32 16,777,216 True Color + Alpha Channel


You will notice that the last entry in the chart is for 32 bits. This is a special graphics mode used by digital video, animation and video games to achieve certain effects. Essentially, 24 bits are used for color and the other 8 bits are used as a separate layer for representing levels of translucency in an object or image.