Question about bizarre differences between `-ts` vs `-ds` about astc-encoder

[solidpixel]

(Edited for clarity)

To make astcenc return the same value for both -ts and -cs, you will need to run the -cs pass with the -decode_unorm8 option specified. Without this you will get LSB rounding differences in the alpha channel. The decode_unorm8 mode is automatically inferred for -ts because it knows the decompressed output is an 8-bit png, but we can't do that inference for -cs so it's defaulting to decode_float16 unless you provide the option.

If you still have issues after that please provide a failing image that reproduces the issue and I can take a look. The behavior above should only cause LSB bit differences, so "totally random-looking bytes" sounds like a different problem.

[solidpixel]

Footnote: The fact that sRGB alpha is specified to decode to decode_float16, when RGB decodes to decode_unorm8, is likely a bug in the Khronos Data Format specification. We currently implement the specified behavior, but the upstream spec may change here (so alpha would become decode_unorm8 by default for sRGB images).

[solidpixel]

Resolved offline - not a compressor issue.