The Practical Zone System for Film and Digital Photography, 6th Edition

Appendix D Bit Depth

Computers store information electronically in the form of a number that at the simplest level can either be 0 or 1. This is called one “bit.” An 8-bit number in a computer has eight digits and is called a “byte.” So, an example of a bit is 0 and a byte is 0000 0000.

Here is how bit depth is notated in digital photography: 8-bit images have a bit depth of 256 levels because if you multiply the number 2 by itself eight times the result is 256 (2, 4, 8, 16, 32, 64, 128, 256).

By this same logic, 12-bit images have a bit depth of 4,096 levels per pixel, and 16-bit images have a bit depth of 65,536 levels per pixel.^* Also, in Adobe Photoshop, for technical reasons, 16-bit images have only 32,769 pixel levels instead of the 65,536 ...