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Diffstat (limited to 'thirdparty/cvtt')
| -rw-r--r-- | thirdparty/cvtt/etc_notes.txt | 27 |
1 files changed, 0 insertions, 27 deletions
diff --git a/thirdparty/cvtt/etc_notes.txt b/thirdparty/cvtt/etc_notes.txt deleted file mode 100644 index bb041a8435..0000000000 --- a/thirdparty/cvtt/etc_notes.txt +++ /dev/null @@ -1,27 +0,0 @@ -The ETC1 compressor uses modified cluster fit: - -Assume that there exists an ideal base color and set of selectors for a given table. -For a given table and set of selectors, the ideal base color can be determined by subtracting the offsets from each pixel and averaging them. -Doing that is equivalent to subtracting the average offset from the average color. -Because positive and negative selectors of the same magnitude cancel out, the search space of possible average offsets is reduced: 57 unique offsets for the first table and 81 for the others. -Most of the offsets result in the same color as another average offset due to quantization of the base color, so those can be de-duplicated. -So: -- Start with a high-precision average color. -- Apply precomputed luma offsets to it. -- Quantize and de-duplicate the base colors. -- Find the ideal selectors for each base color. - -Differential mode is solved by just finding the best legal combination from those attempts. - -There are several scenarios where this is not ideal: -- Clamping behavior can sometimes be leveraged for a more accurate block. -- Differentials can sometimes be moved slightly closer to become legal. -- This only works when MSE is the error metric (i.e. not normal maps) -- This only works when pixel weights are of equal importance (i.e. not using weight by alpha or edge deblocking) - -T and H mode just work by generating clustering assignments by computing a chrominance line and splitting the block in half by the chrominance midpoint and using those to determine the averages. - -Planar mode is just solved algebraically. - -If you want to emulate etc2comp's default settings, add the flag ETC_UseFakeBT709 to use its modified Rec. 709 error coefficients. -Doing that will significantly slow down encoding because it requires much more complicated quantization math.
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