25 How does colour depth (bit planes) relate to the number of colours?
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This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
25 How does colour depth (bit planes) relate to the number of colours?
[From: Michael Scott (scott@bme.ri.ccf.org)]
To understand this (and it isn't that difficult) you have to know what the binary (or base 2) number system is. Instead of each digit in a number varying between 0 and 9, the values can only be 0 or 1. This means that for a given digit, there are only two possible options. So, for say a 4 digit binary value, there are 4^2 (or 2x2x2x2) or 16 unique values. Now it becomes easy to translate between the number of bit planes (that's number of binary digits) and number of colours.
number of colours = 2^(# of bit planes) resulting in: 1 bit = 2 colours, 2 bit = 4 colours, 4 bit = 16 colours 8 bit = 256 colours, 15 bit = 32k, 16 bit = 64k, 24 bit = 16.7M
Note that the maximum colour depth at a given pixel addressability is limited by the video controller, not the monitor, since almost all modern monitors are analog.
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