Page 53 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 4: Image

There are a number of interesting attributes of such a colour indexing system. If there are less than notes
256 colours in the image then this bitmap will be the same quality as a 24 bit bitmap but it can
be stored with one third the data. Interesting colouring and animation effects can be achieved by
simply modifying the palette, this immediately changes the appearance of the bitmap and with
careful design can lead to intentional changes in the visual appearance of the bitmap.
A common operation that reduces the size of large 24 bit bitmaps is to convert them to indexed
colour with an optimized palette, that is, a palette which best represents the colours available in
the bitmap.
4 bit indexed colour
This is identical to 8 bit colour except now only half a byte; 4 bits are used for the index. This
supports a table of up to 16 colours (See Figure 4.7).

figure 4.7: 4 Bit indexed Colour

32 bit rGB

This is normally the same as 24 bit colour but with an extra 8 bit bitmap known as an alpha channel.
This channel can be used to create masked areas or represent transparency (See Figure 4.8).

figure 4.8: 32 Bit rGB

16 bit rGB

This is generally a direct system with 5 bits per colour component and a 1 bit alpha channel
(See Figure 4.9).

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