ICBC - A High Quality BC1 Encoder
This is the BC1 texture block encoder used by NVTT, extracted as an easy to use single header file library.
It implements several algorithms:
- Fast DXT encoding using box fitting as described in: Real-Time-YCoCg-DXT-Compression
- Least squares endpoint optimization as in stb_dxt: https://github.com/nothings/stb/blob/master/stb_dxt.h
- Exhaustive cluster fit evaluation as in squish: http://sjbrown.co.uk/2006/01/19/dxt-compression-techniques/
- Iterative end-point refinement along the lines of the algorithm described by clooom: http://cbloomrants.blogspot.com/2008/12/12-08-08-dxtc-summary.html
There are also some experimental algorithms that are not enabled:
- Exhaustive cluster fit with pre-computed factors for every cluster configuration. As in High Quality DXT Compression using CUDA
- K-means cluster fit.
Even though NVTT contained some fast compressors, these were not particularly optimized. The focus was on producing very high quality textures, and for a long time this was the highest quality open-source compressor available.
Today it has been superseded by Rich Geldreich's RGBCX library, which I hope becomes a suitable replacement for this code in almost all scenarios.
Results
The following chart shows the average PSNR of different BC1 compressors and different configurations on the Kodim and Waterloo image sets plotted against the time it took to encode them:
- stb is stb_dxt version 1.09 with various improvements that Rich and I have proposed.
- RGBCx is version 1.12 levels 0 to 18 with
allow_3coloranduse_transparent_texels_for_blackenabled. - squish is version 1.15
- amd is AMD's CMP_Core V3.2.4691
- ICBC is version 1.0 compiled with SSE2 support and
ICBC_FAST_CLUSTER_FITenabled.
This other chart shows similar results, on a texture set from my employer:
