1.2.2. Colour Depth

A bit is the basic information unit used in computing theory and practice. A single bit can represent two states, normally 0 / 1 or true / false. In our case a single bit allows us to distinguish two different colours. Often these will be considered black and white. With n bits we are able to produce 2ⁿ colours. 4 bits for example allow to represent 16 different colours. Therefore the colour depth of an image tells us how many colours are used to visualise the image.

Very often one byte (one byte is composed of 8 bits) is used for each primary colour (e.g. red, green and blue). Thus, the range of every colour is 2⁸ = 256 and it therefore goes from 0 to 255, whereas 0 stands for the lowest and 255 for the highest intensity. Consequently, by combining all primary colours, 2⁸*2⁸*2⁸ or 256*256*256 = 16.777.216 different colours can be produced.

The following colour depths are most common:

Colour Depth	Name	Code	Number of Presentable Colours	Example Picture
1 Bit	Black and White	Black: 1 Bit	2
8 Bit	Greyscale	Black: 8 Bit	256
16 Bit	High Colour	Red: 5 Bit Green: 5 Bit Blue: 6 Bit	216 = 65'536
24 Bit	True Colour	1 Byte (8 Bits) per R, G and B	224 = 16'777'216
32 Bit	True Colour with 8-Bit channel	1 Byte (8 Bits) per R, G, B and α (α includes a value for the transparency of the pixel)	224 = 16'777'216 + α