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Author Topic: Decompressing compressed graphics  (Read 1279 times)

CDiablo

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Decompressing compressed graphics
« on: July 14, 2015, 12:31:32 pm »
So, Im working on PC Engine stuff, most games(roughly 9/10) do not work in any graphics editors and thus are likely compressed. I am trying out how to figure out to do so and I want to make sure I am on the right track. So what I am doing is learning 6502 ASM, then learn the concepts of the HU6280, learn the concepts of compressions that are traditionally used, undo the compression, make the changes I want then recompress or pad the rom to an acceptable size. So am I on the right track? Am I over/under complicating things? Thanks for the help all.

FAST6191

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Re: Decompressing compressed graphics
« Reply #1 on: July 14, 2015, 04:48:22 pm »
I would say you are overcomplicating things. Most compression can be handled with basic instructions, and usually is on the old systems as they tend not to have dedicate decompression/media type instructions,

https://ece.uwaterloo.ca/~ece611/LempelZiv.pdf if my usual link for an intro to compression. It mainly handles the LZ family but it covers huffman and other things you might commonly see enough that you can probably figure out what goes. Though with 8 bit systems you are often looking at something even more simple like run length encoding (kind of a simplification of LZ).

Once you have figured out the family and specific implementation (usually a different kind of flag or different split in the length/distance combo for LZ, utterly breaks an existing decompression tool but if you have source it able to be changed more quickly than you will probably be able to compile it.