DuneGraph file format

DuneGraph         *.DG1, *.DC1

The *.DGU is a simple uncompressed format:
    3 bytes       'DGU' file ID ($444755)
    1 byte        version number (1)
    1 word        xres (320)
    1 word        yres (200)
  256 long        palette, Falcon format, RG0B
64000 bytes       picture data, 320x200, 8 bitplanes (other resolutions have not been seen)

The *.DC1 is a simple compressed format:
    3 bytes       'DGC' file ID  ($444743)
    1 byte         packing method (0, 1, 2 or 3)
    1 word        xres
    1 word        yres
    1 word        unknown ($00ff)
  256 long        palette, Falcon format, RG0B
  ??? bytes       compressed picture data
Compressed picture data:
Method 0: no compression, 64000 bytes, 320x200, 8 bitplanes
For method 1 to 3 the bit planes are unmixed, so first you get all
data for bit plane 0, then bit plane one etc.
Method 1: simple runlength on byte level
     1 long       size of compressed data, including this long
     do
       1 byte       repeat count
       1 byte       data
       write (repeat count+1) times data
     until you run out of compressed data
Method 2: simple runlength on word level
     1 long       size of compressed data, including this long
     do
       1 word       repeat count
       1 word       data
       write (repeat count+1) times data
     until you run out of compressed data
Method 3: simple runlength on long level
     1 long       size of compressed data, including this long
     do
       1 word       repeat count
       1 long       data
       write (repeat count+1) times data
     until you run out of compressed data

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