What is bit-depth?

Bit depth is an enormously important facet of computer systems. In simple terms, bit-depth expresses the number of bits in a byte.

For example ... a byte made up of 8 bits (eg "10011101") has a bit-depth of 8. We can also say this byte is 8-bit.

Possible values of a byte

Bit-depth determines the number of possible variations a byte can be. For example, there are 16 possible variations in a 4-bit byte ...

Byte (binary)	Equivalent decimal value
0000	0
0001	1
0010	2
0011	3
0100	4
0101	5
0110	6
0111	7
1000	8
1001	9
1010	10
1011	11
1100	12
1101	13
1110	14
1111	15

See computer counting systems for more on base 2 (binary) and base 10 (decimal) counting systems

Here are some other typical bit-depth values ...

Bit depth	Byte length	Example Byte	Possible values	No of values
1	1 bit	1	1 and 0	2
8	8 bits	10010011	00000000 to 11111111	256
16	16 bits	1001001110010011	00000000 - 00000000 to 11111111-11111111	65,536
24	24 bits	100100111001-001100111010	00000000 - 00000000 - 00000000 to 11111111- 11111111-11111111	Millions!

Bit-depth and quality

As a general rule ...

The higher the bit-depth the better the quality, but ... the bigger the file size, and the greater the processing power required to handle it.
The lower the bit-depth the poorer the quality, but ... the smaller the file size, and the lesser the processing power required to handle it.

Differing bit-depths

Different software elements in a single computer system can have different bit depths. For example ...

A GIF image file may be made up from 8-bit (or less) bytes
A CD quality .aif or .wav audio file will be made up of 16-bit bytes
A native Photoshop document will usually be 24-bit
Elements of the Mac OSX system are 64-bit

It is possible for a single program to handle different media files of different bit depths simultaneously. For example ... Director can replay audio, display images and play video files of different bit depths.