file format.txt

Format details:

first byte -- header. image width (in tiles)

next bytes -- runs. type of run described by the two least significant bits of the first byte of each run
              according to the folowing:

%nnnnnn01  -- dd : run of n+2 (2 to 65) *same word* value HHdd (a.k.a. "normal" RLE)
%nnnnnn11  -- dd : run of n+2 (2 to 65) *successive word* values (HHdd, HHdd+1, HHdd+2 ...)
                 : will eventually change HH too!
%nnnnnn00  -- dd kk pp [...] : run of n (1 to 63) words using each of the following bytes (HHdd, HHkk, HHpp...) 
                             : n=0 means end of compressed data
%hhhhht10   : set new HH to %000hhhhh 
      t = 1 : set the value temporarily (revert to previous value after next run) 
      t = 0 : set it permanently
(HH is initialized to $00 at launch, both on compressor and on decompressor)