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Displaying Colour

Colour displays can vary quite a lot although they generally fall into a few classes:

Black/White
- where 1 bit per pixel is used. The bits are sometimes called planes.
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.

Colourmaps

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


Dave.Marshall@cm.cf.ac.uk
Tue May 24 16:52:56 BST 1994