Alexander Suvorov 1ef829ed6f Move alpha endpoint refinement into the alpha endpoint optimization thread ...

This change improves compression speed when using alpha channel.

Explanation:
As the alpha endpoint refinement does not depend on the alpha selector codebook computation, it can be safely moved into the alpha endpoint optimization thread.

Testing:
The modified algorithm has been tested on the Kodak test set using 64-bit build with default settings (running on Windows 10, i7-4790, 3.6GHz). All the decompressed test images are identical to the images being compressed and decompressed using original version of Crunch.

[Compressing Kodak set without mipmaps]
Original: 1582222 bytes / 28.912 sec
Modified: 1494501 bytes / 24.128 sec
Improvement: 5.54% (compression ratio) / 16.55% (compression time)

[Compressing Kodak set with mipmaps]
Original: 2065243 bytes / 36.985 sec
Modified: 1945365 bytes / 31.741 sec
Improvement: 5.80% (compression ratio) / 14.18% (compression time)

2017-05-12 14:06:53 +02:00

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