This change improves the compression speed for DXT encoding.
Explanation:
The main ideas used for the DXT endpoints computation optimization:
- Instead of using map in tree clusterizer, the source vectors can be stored in an array and sorted before the quantization. This might increase the amount of used memory, but is much more efficient in terms of memory reallocation.
- Endpoint caching can be used throughout the color endpoint computation, and not just within the optimize_endpoints function. The only place where endpoint caching can not be used is the final step of the try_combinatorial_encoding function, where alternate rounding is used.
- When computing endpoint codebooks, endpoint optimizer and endpoint refiner can be reused, which eliminates unnecessary memory reallocations.
DXT 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 (revision ea9b8d8).
[Compressing Kodak set without mipmaps using DXT1 encoding]
Original: 1582222 bytes / 28.879 sec
Modified: 1468204 bytes / 11.099 sec
Improvement: 7.21% (compression ratio) / 61.57% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.919 sec
Modified: 1914805 bytes / 14.621 sec
Improvement: 7.28% (compression ratio) / 60.40% (compression time)
ETC 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). The ETC1 quantization parameters have been selected in such a way, so that ETC1 compression gives approximately the same average Luma PSNR as the corresponding DXT1 compression (which is equal to 34.044 dB for the Kodak test set compressed without mipmaps using DXT1 encoding and default quality settings).
[Compressing Kodak set without mipmaps using ETC1 encoding]
Total size: 1607858 bytes
Total time: 17.108 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
Alexander Suvorov
3053c9dd93