This coding scheme applies to rectangular raster images made up of raster points that are either set or not set. This coding scheme does not support any notion of colour. Image data are coded as follows:

Byte(s)	Description	Length
1	image width = X	1
2	image height = Y	1
3 to K+2	image body	K

 

This coding scheme applies to coloured rectangular raster images. Raster image point colours are defined as references into a colour look-up table (CLUT), which contains a subset of the red-green-blue colour space. The CLUT in turn is located in the same transparent file as the image instance data themselves, at an offset defined within the image instance data. Image data are coded as follows:

Byte(s)	Description	Length
1	Image width = X	1
2	Image height = Y	1
3	Bits per raster image point = B	1
4	Number of CLUT entries = C	1
5 to 6	Location of CLUT (Colour Look-up Table)	2
7 to K+6	Image body	K

  The CLUT (Colour Look-up Table) for an image instance with C colours is defined as follows: Contents:

• C CLUT entries defining one colour each.

Coding:

• the C CLUT entries are arranged sequentially:

  Byte(s) of CLUT	CLUT Entry
  1-3	entry 0
  ...	...
  3*(C-1) +1 to 3*C	Entry C-1

   
  Each CLUT entry in turn comprises 3 bytes defining one colour in the red-green-blue colour space:

  Byte(s) of CLUT entry	Intensity of Colour
  1	Red
  2	Green
  3	Blue

   

A value of 'FF' means maximum intensity, so the definition 'FF' '00' 00' stands for fully saturated red.

This coding scheme is identical to the Colour Image Coding Scheme as defined in appendix B.2, with the following exception:

• Entry number C-1 in the colour look-up table (CLUT), where C is the number of entries in the CLUT, defines transparency. Raster image points which point to this entry are transparent, so that the underlying colour in the display is shown.

The three colour-coding bytes of entry number C-1 in the CLUT are of no importance when referenced from images using the '22' coding scheme.