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Colour displays can vary quite a lot although they generally fall into a few
- - where 1 bit per pixel is used. The bits are sometimes
- True Colour or Full Colour
- - 24 bits per pixel (8 bits each for RGB) are
used to display around 16.5 million possible colours.
- 8-bit displays
- - True colour displays tend to expensive as they need a
lot of memory and involve more complex programming. 8-bit displays are the most
common. These are capable of only supporting 256 colours at any one time.
However 256 colours can be chosen form the whole palette of the True colour
range. Colourmaps or colour look up tables are used to enable this.
A colourmap consists of (256) cells each of which contains 8 bit red, green
and blue values.
A pixel value in an image or on the screen basically provides an index to the
colourmap which says how to render the appropriate colour.
Fig. 26 Colourmaps and pixels