BC1-3 Compressor single color optimization

The libsquish library adds a special-case block compression for DXT when all 16 source pixels in the block are the same color.

For this case, it uses a table-based scheme to pick the optimal encoding.

NVTT adopted the same solution.

Algorithm discussed in this blog

Q: What do to about dithering with the single-color blocks?

Any news about this? I'm trying to batch convert a bunch of images using a C# wrapper of this library but I'm getting the typical green-ish artifacts in every DXT1/DXT5, there's a workaround that can be done through code or something like that?

This issue is specifically for compressing 4x4 blocks that all contain exactly the same color. BC1-3 (a.k.a. DXT1-5) all use 5:6:5 for RGB so that sometimes can make the result be a little green tinted depending on the input values.

By default the DXT1-5 compressor is using a 'luminance perceptual' weighting for the colors. You could try TEX_COMPRESS_UNIFORM (which for texconv is -bc u switch). It could also be the result of SRGB vs. Linear color space mix ups.

Using TEX_COMPRESS_FLAGS.UNIFORM doesn't change anything, getting the same artifacts as always.
I tried using almost every combination of WIC_FLAGS and TEX_COMPRESS_FLAGS
PD: The wrapper is using the March 2024 version of the lib.

ScratchImage image = TexHelper.Instance.LoadFromWICFile("Original.png", WIC_FLAGS.NONE);
ScratchImage compressed = image.Compress(DXGI_FORMAT.BC1_UNORM, TEX_COMPRESS_FLAGS.UNIFORM, 0.5f);
compressed.SaveToDDSFile(DDS_FLAGS.NONE, "Compressed.dds");

Can you attach the original.png?

Sure:
Image

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BC1-3 Compressor single color optimization #223

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BC1-3 Compressor single color optimization #223

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walbourn commented on Mar 4, 2021

walbourn commented on Jun 9, 2021

Hancapo commented on Aug 12, 2024

walbourn commented on Aug 12, 2024

Hancapo commented on Aug 13, 2024

walbourn commented on Aug 13, 2024

Hancapo commented on Aug 13, 2024

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