Some textures appear significantly lower quality than others about basis_universal HOT 6 OPEN

(Note: we recognize this is likely the same issue as #41 - but still wondering if there are any potential improvements to be had in cases like this. Thanks very much in advance for looking.)

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Same issue.. I compressed using compressonator to ETC1, so color mismatch is probaly not a basis issue - it's ETC1 issue, so transcoding to something better (maybe to BC5 or 7) on desktop would be preferrable. Let it occupy more space on videocard but correct colors seem more important

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This texture has highly saturated gradients that occur over small spatial areas, which is one of ETC1S's key weaknesses. ETC1S can't encode saturated gradients at the pixel level, because it can only vary the luma within a block. For a red gradient, we can't vary the luma within the block because that would cause the pixels to become desaturated away from red.

Full ETC1 would look a little better, because it has 4x2 or 2x4 subblocks, but it still would have some blockiness at the subblock level. This problem is particularly obvious on some videos.

One workaround for problems like this is to enlarge the source texture, by 200 or 400%, then encode that. The gradient would then be spread between more blocks, but this will cost bitrate and increase transcode time.

For the 3rd major Basis Universal milestone we are adding a higher quality mode to the system. We're not exactly sure what we're going to do yet, but we'll definitely be fixing this problem.

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Thanks for the detailed breakdown of the problem!

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@richgel999 I'm really looking forward to higher quality mode, please update if you have any news about it.
In my case, I want to use Basis for lightmap but the artifacts and color banding are too much to be useable, even at the highest quality (the quality seems to be degraded a lot compared to DXT1?).

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We hear you! We're working on a system that uses a very strong subset of ASTC as a base, which can be transcoded to a variety of formats. It'll be a lot higher quality than the ETC1S system that basisu uses today.

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