Bit-depth by Matt Ottewill

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.

Bit depth and audio

Click here to read how bit-depth effects quality in an audio file.

Bit depth and images

Click here to read how bit-depth effects quality in an image file.

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