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0 pointsgaraetjjte5y ago0 comments

>and even BCn, can't be compressed much further

S3TC is block compression, so if there is repeating data in images it will compress quite well.

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gens5y ago

I tried compressing BC7 (from AMD-s Compressonator) using lz4c and it wasn't much.

Just re-ran it (with -hc, version 1.9.3(latest now)) and: "Compressed 5592544 bytes into 5413783 bytes ==> 96.80%".

7z with "7z a -mx=9 -t7z asd.7z albedo_PNG_BC7_1.KTX" does 5592544 bytes to 4844707 bytes (down to ~87%).

Original file is 10227047 bytes (PNG, RGBA), i can't remember if the ktx has mipmaps.

EDIT: Note that the image is fairly noisy (gravel). Could/should be better with more "artificial" textures.

I don't know if ktx does some extra compression, but, looking at it, i doubt it.

PS I think that BC could be massaged at compression to be better compressible, and i think i read something about that. Don't remember.

garaetjjteOP5y ago

Yes, it depends on content and won't do much for grainy surfaces. I don't have AAA game quality textures to compare, but I think for usual textured model it is still worthwhile. eg. this https://milek7.pl/.stuff/somelocotex.png weights 16MiB uncompressed, 5.1MiB as PNG, 5.3MiB as DXT5, and 2.1MiB as DXT5-in-LZ4. (mipmaps included in DXT5)

>PS I think that BC could be massaged at compression to be better compressible, and i think i read something about that. Don't remember.

There's Oodle BC7Prep from RAD Game Tools: http://www.radgametools.com/oodletexture.htm

EDIT: RAD page states that "BC7 blocks that are often very difficult to compress", so that might be also a factor why my DXT5 test compressed much better than your BC7.

EDIT2: Yeah, with BC7 LZ4 only compresses it down to 4.6MiB.

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