Any "bit" number is 2 to the power of that number. For example, 8-bit is 2 to the power of 8, or 256. So an 8-bit image can use up to 256 colors. 1 bit is 2 colors, 16-bit is 65,356 colors and 32-bit is a whopping 4,294,967,296 colors. You can figure out the other bit values.

The reason for the powers of two is technical. Basically, a pixel in a 1-bit image uses the smallest unit of memory, a bit. The single bit can either be "on" or "off", 1 or 0, true or false, black or white. There are only two unique configurations of the single bit, so it can only contain two unique colors. A 2-bit image can use four colors, so a single two-bit pixel uses, you guessed it, two bits of memory. The possible configurations of two bits of memory are:

1) 00
2) 01
3) 10
4) 11

Since it can contain 4 unique settings, it can contain 4 unique colors, and so on up the bit values. And believe it or not, everything on your computer is made up of these little 1s and 0s.

I know this is probably way more technical than what you were after, and I know I haven't explained it well. hopefully someone else can make it clearer (I need an editor :P).

Edited by Hatch - 06 July 2009 at 12:23pm

Well, if you think about Hatch's answer as being the definition of 8 bits, then 8 bits = pic with 256 colors. Pic with 256 colors aint really crappy graphics, is it?

yerp, the bit numbers that video game console companies made such a big deal about didn't actually matter much to the consumer. They were just marketing bluster.

So then 4 bit is only 16 colors, 3 bit is only 8 colors, etc. Ok I get it now, Thanks for the replies.