A true colour digital image requires 24-bits to specify
the colour of each pixel on the screen. This is one of the
simple standard colour formats used for transferring image
data from a video source to a display device. It is very
advantageous to operate directly on the 24-bit image for-
mat since this is a standard output from many video
sources (CD/DVD player and VGA card). Only an ana-
logue to digital converter (ADC) chip is required to per-
form the task of signal conversion. The digital output
can then be used for further processing. The drawback is
that it is expensive to have a high-speed memory to support
such a full-colour display on a high resolution display. An
alternative solution is to provide a limited number of bits
for specifying the colour of each pixel. Each of these values
is then used as an index into a user defined colour table