Texture (ktx2) compression quality is awful

[MAG-AdrianMeredith]

I was hoping to use KTX compression (either etc1s or uastc) however the results are unusable regardless of what settings I use (which seem to make very little difference). Is there no way to get right of the obvious blocking artifacts?
This is with this command

gltf-transform uastc MinimalGallery_512.glb mg.glb --rdo --level 4 --slots "lightmapTexture" --rdo-std-dev 65535 --rdo-lambda 0.001 --rdo-block-scale 300 --config ./lightmap.js

before

after

[donmccurdy]

I'm not a particular expert in GPU compression codecs, but to maximize quality I think you would want to use UASTC, and to disable RDO (--rdo false).

For debugging, if you run the command with --verbose then glTF Transform will also print the internal CLI calls to the KTX Software CLI. If you're having trouble with particular textures, it might be worth extracting a 'problem' texture, compressing it independently with the KTX Software CLI, and then decoding back to PNG to check the results. Perhaps you may find a better combination of options for this input.

[MAG-AdrianMeredith]

Thanks for the reply, this isn't a slight on gltf-transform its amazing. What I'm more looking for is a sense of expectations. Is this just how it is or is there some sort of parameter to increase quality? it appears not :(. I have noted that other models appear to look better than this one. The artifacts just seem non sensical to me (almost like they are inverted with the lighter part closer to the dark part and vice versa)

[donmccurdy]

GPU compression formats are block-based: for example groups of 4x4 or 6x6 pixels are encoded as a group, and within that group the pixels are represented partitions, not individual pixels. When there are compression quality issues in any GPU-based format, it's normal that the artifacts correspond with the block layout. That said, this particular results looks worse than I'd expect for UASTC.

An additional consideration with Basis Universal is that we're compressing into one format (ASTC-based, for UASTC) but then transcoding at runtime into a format the GPU supports, which might be different and lower quality. If the viewer/engine you're using has chosen to transcode UASTC to a low-quality target format like ETC1/2 (for whatever reason), the quality you see in the viewer might be less than what is available in the file. The CLI ktx extract command can be helpful for decompressing the file losslessly to see what's there before transcoding.

Many parameters affect quality: RDO in particular is a post-process after GPU compression that will (to my knowledge) always make quality worse in exchange for improving filesize with ZSTD, Gzip, or other supercompression.