QuoteLarger ones seem to be chunked, LZ compressed and run length encoded, and I wasn't able to figure out uncompressing them.
okay, after spending about a week on this problem here's where we are.
I think I'm close to figuring out the compression/chunked data format of the image files.
here's the output I got for Imagery/Misc/dragonent for example:
As you can see, it's not quite correct yet, but you can still kinda see a dragon there, it's just the chunks are incorrectly aligned or appear scewed.
Here's another example Imagery/Forest/forbirch001:
Again, you can kinda see a birch tree here. but the pixels are not aligned properly.
What this tells me is that the decompression of each chunk works more or less as it should (I based it on ASM code in https://github.com/benjcooley/Revenant/blob/83f806bb65b762b2cc3e1ea509010f05342caa12/chunkcache.cpp#L249). The part that is missing is chunk alignment/sizing.
On another note, I'm also having some troubles with palletes for 8bit images.
For example, here's Imagery/Misc/blueflower:
As you can see, it's not blue, but a yellow in fact.
Here's another example Imagery/Misc/bread:
Again, not quite the color of bread.
The thing is, I'm short on time ATM, so unfortunately, I have to stop here for now. Maybe I will pick this up later when I have more free time
In case, anyone would like to continue or learn from my efforts, I've uploaded my JS code to Github: https://github.com/WiegerWolf/revenant-map-builder and also attaching it to this post. It's a single long js file for Node.js.
main.js.txt (mirror https://pastebin.com/UY7cbc2w)
Oh and I also found this https://github.com/IgorZyktin/Revenant which contains some useful things too in python