This change improves the compression speed for DXT encoding.
Explanation:
In order to evaluate an endpoint solution, it is necessary to compute the sum of the squared distances from the source pixels to their nearest block colors, defined by the evaluated endpoint solution. Such computation is quite complicated, so before it is performed, we can compute the sum of the squared distances from the source pixels to the axis-aligned bounding box enclosing all the evaluated block colors (if the source pixel appears to be inside the AABB of the evaluated solution, then the distance is considered to be 0). If the sum of the squared distances to the AABB of the current solution is already bigger than the sum of the squared distances computed for the previously found best solution, then the current solution does not need to be evaluated.
The actual trick here is that the sum of the squared distances to the AABB of the current solution can be computed in constant time using the following approach. The sums of the squared distances for each color component can be computed separately. For each color component the AABB determines 2 planes: the "lower" plane, defined by the lower boundary of the AABB, and the "upper" plane, defined by the upper boundary of the AABB. The sum for each color component is combined from two parts: the sum of the squared distances from the lower plane to all the source pixels which are below the lower plane, and the sum of the squared distances from the upper plane to all the source pixels which are above the upper plane. Considering that the endpoints of the evaluated solution are encoded as RGB565, there are 32 possible planes for the red and blue components, and 64 possible planes for the green component. For each plane it is sufficient to precompute the following two values: the sum of the squared distances from the plane to all the source pixels which are "below" this plane, and the sum of the squared distances from the plane to all the source pixels which are "above" this plane. The total sum of the squared distances from the source pixels to any evaluated AABB can then be represented as a sum of 6 precomputed values, while all the used values can be precomputed in linear time with dynamic programming.
Note: The AABB check seems to work faster than inserting a solution into the hash map. For this reason the AABB check is performed first.
Additional improvements: A few minor adjustments have been made in order to make sure that the texture decompression gives identical result to the original version of Crunch also for 32-bit builds (original Crunch library uses different floating point models for 32-bit and 64-bit builds).
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 / 28.861 sec
Modified: 1468204 bytes / 8.622 sec
Improvement: 7.21% (compression ratio) / 70.13% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.980 sec
Modified: 1914805 bytes / 11.294 sec
Improvement: 7.28% (compression ratio) / 69.46% (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: 15.529 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
This change improves the compression speed for both DXT and ETC encodings.
Explanation:
The vectors which are processed in the cluster indices computation step, are the very same vectors which were used in the vector quantization step. This means that every processed vector already has a specific centroid associated with it. Even though the associated centroid is not necessarily the closest one to the processed vector, the distance to the associated centroid can be used as an upper boundary of the distance to the closest centroid. This allows to efficiently perform early out while computing the distances to the other centroids.
Note: The modified algorithm is supposed to generate decompression result identical to the original version of Crunch. For this reason the centroid associated with a specific training vector is not used as an initial best solution, because it could potentially change the decompression result in cases when the processed training vector is equidistant from multiple centroids (selection of the closest centroid in such cases depends on the processing order).
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 / 28.847 sec
Modified: 1468204 bytes / 8.929 sec
Improvement: 7.21% (compression ratio) / 69.05% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.953 sec
Modified: 1914805 bytes / 11.651 sec
Improvement: 7.28% (compression ratio) / 68.47% (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: 15.695 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
This change improves the compression speed for both DXT and ETC encodings.
Explanation:
The main ideas used for optimization of the vector quantization algorithm:
- intermediate structures can store vector indices instead of the vector data, which minimizes the total amount of copied data when splitting a node (this is especially important for selector quantization, where processed vectors have 16 components)
- weighted vectors and weighted dot products can be cached
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 / 28.893 sec
Modified: 1468204 bytes / 9.310 sec
Improvement: 7.21% (compression ratio) / 67.78% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.942 sec
Modified: 1914805 bytes / 12.232 sec
Improvement: 7.28% (compression ratio) / 66.89% (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: 16.121 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
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
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 / 28.866 sec
Modified: 1468204 bytes / 11.858 sec
Improvement: 7.21% (compression ratio) / 58.92% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.878 sec
Modified: 1914805 bytes / 15.625 sec
Improvement: 7.28% (compression ratio) / 57.63% (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: 17.181 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
Alexander Suvorov
richgel99@gmail.com