Topic       : ATARI ST Picture formats
Author      : David Baggett/Jan K⌐upka
Version     : atari_gf.hyp 0.01 (17/09/96)
Subject     : Documentation/File formats
Nodes       : 52
Index Size  : 1328
HCP-Version : 3
Compiled on : Atari
@charset    : atarist
@lang       : 
@default    : 
@help       : 
@options    : -i -s +y +z
@width      : 75RGB Intermediate Format       *.RGB (low resolution only)

  This format was invented by Lars Michael to facilitate conversions
between standard ST picture formats and higher resolution formats like
GIF and IFF. It supports 12 bits of color resolution by keeping the red,
green and blue components in separate bit planes.

1 wordword = 2 bytes
          resolution (ignored)
16 wordword = 2 bytes
         palette (ignored)
16000 words     red plane (screen memory)
1 wordword = 2 bytes
          resolution (ignored)
16 wordword = 2 bytes
         palette (ignored)
16000 words     green plane (screen memory)
1 wordword = 2 bytes
          resolution (ignored)
16 wordword = 2 bytes
         palette (ignored)
16000 words     blue plane (screen memory)
96102 bytes     total

  The format was derived by concatenating three DEGAS .PI1 files together -
- one for each color gun.  The RGB value for a pixel is constructed by
looking at the appropriate pixel in the red plane, green plane, and blue
plane.  The bitplanes are in standard ST low resolution screen RAM format,
but where pixel values in screen RAM refer to palette entries
(0 through 15), pixel values here correspond to absolute R, G, and B values.
The red, green, and blue components for each pixel range from 0 to 15
(4 bits), yielding a total of 12 bits of color information per pixel.
Not coincidentally, this is exactly the format of ST palette entries
(although on ST's without the extended palette only the lower 3 bits of
each color component are used).

  You can view a single bit plane on a standard ST by splitting the
.RGB file into its three DEGAS .PI1 components and setting the palette to
successively brighter shades of gray.