On some screen codecs

Recently my attention was drawn to two screen codecs. So I’ve looked a bit closer at them (I’m not going to implement them — at least now, simian audio codec is waiting) and here are the most interesting bits to me.

Dxtory codec. I don’t know if it uses prediction or not but the coding is extremely simple: read unary code (1-8 bits), if the code is 8 (escape) then read byte for a new value, otherwise retrieve value from LRU list and of course move/put the new value to the beginning of that list.
The organisation into slices and decoding for different colourspaces is trivial.

Mirillis FIC Video. This one has more complexity: it operates on 8×8 blocks. Block is coded in the following way: if the flag is present then the block is skipped, otherwise read 7 bits for the number of coefficients to decode and the coefficients (signed exp-Golomb coded). Zigzag scan, IDCT, output.


2 Responses to “On some screen codecs”

  1. compn says:

    whatever happened to apple intermediate codec ICOD ?

  2. Kostya says:

    Absolutely nothing, it still waits for someone to RE it or finish its REing actually.