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Enhance README with XUASTC and ASTC options

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Added more detailed options for XUASTC LDR compression and clarified ASTC LDR support.
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Rich Geldreich
2026-01-24 20:50:26 -05:00
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parent 1b2dec57fc
commit 4edf014f34
1 changed files with 12 additions and 4 deletions
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@@ -242,11 +242,19 @@ Compressing and Unpacking .KTX2/.basis Files
`basisu -xuastc_ldr_6x6 -quality 75 -effort 4 x.png`
An alias for `-xuastc_ldr_6x6` is `-ldr_6x6i` (where 'i'="intermediate").
An alias for `-xuastc_ldr_6x6` is `-ldr_6x6i` (where 'i'="intermediate"). All [14 standard ASTC block sizes](https://developer.nvidia.com/astc-texture-compression-for-game-assets) are supported, from 4x4-12x12: 4x4, 5x4, 5x5, 6x5, 6x6, 8x5, 8x6, 10x5, 10x6, 8x8, 10x8, 10x10, 12x10 and 12x12. The XUASTC LDR to BC7 transcoder has special optimizations for several common block sizes: 4x4, 6x6 and 8x6. When transcoding XUASTC LDR at these particular block sizes, most XUASTC blocks are *directly* transcoded to BC7, skipping the real-time analytical bc7f encoding step.
The options `-xuastc_arith`, `-xuastc_zstd` (the default), and `-xuastc_hybrid` control the XUASTC LDR profile used. The arithmetic profile trades off transcoding throughput for 5-18% better compression vs. the Zstd profile, and the hybrid profile is a balance between the two.
More ASTC and XUASTC LDR specific options:
All [14 standard ASTC block sizes](https://developer.nvidia.com/astc-texture-compression-for-game-assets) are supported, from 4x4-12x12: 4x4, 5x4, 5x5, 6x5, 6x6, 8x5, 8x6, 10x5, 10x6, 8x8, 10x8, 10x10, 12x10 and 12x12. The XUASTC LDR to BC7 transcoder has special optimizations for several common block sizes: 4x4, 6x6 and 8x6. When transcoding XUASTC LDR at these particular block sizes, most XUASTC blocks are *directly* transcoded to BC7, skipping the real-time analytical bc7f encoding step.
- The options `-xuastc_arith`, `-xuastc_zstd` (the default), and `-xuastc_hybrid` control the XUASTC LDR profile used. The arithmetic profile trades off transcoding throughput for 5-18% better compression vs. the Zstd profile, and the hybrid profile is a balance between the two.
- `-ts` or `-srgb` enables the sRGB profile (the default), and `-tl` or `-linear` enables the linear profile.
- `-weights X Y Z W` sets the unsigned channel error weights, used to favor certain channels during compression.
- Another set of XUASTC specific options overrides the windowed RDO behavior (windowed RDO is a separate and optional perceptual optimization vs. Weight Grid DCT): `-xy` enables and `-xyd` disables windowed RDO. By default, if Weight Grid DCT is not enabled (i.e. `-quality` isn't specified, or its set to 100), windowed RDO is disabled. Windowed RDO is automatically enabled if the quality level is less than 100, unless `-xyd` is specified. Also see the tool's help text for additional windowed RDO options: `-ls_min_psnr`, `-ls_min_alpha_psnr`, '-ls_thresh_psnr`, '-ls_thresh_alpha_psnr`, etc.
- `-xs` disables 2-3 subset usage and `-xp` disables dual plane usage (slightly higher compression and faster transcoding to BC7).
- To compress an LDR sRGB image to a standard ASTC LDR 6x6 .KTX2 file, using effort level 4 (valid effort levels 0-10):
@@ -254,7 +262,7 @@ All [14 standard ASTC block sizes](https://developer.nvidia.com/astc-texture-com
An alias for `-astc_ldr_6x6` is `-ldr_6x6`.
All 14 standard ASTC block sizes are supported, from 4x4-12x12. Internally the XUASTC LDR encoder is used, but standard ASTC block data is output, instead of supercompressed XUASTC LDR.
Just like XUASTC LDR, all 14 standard ASTC block sizes are supported, from 4x4-12x12. Internally the XUASTC LDR encoder is used, but standard ASTC block data is output, instead of supercompressed XUASTC LDR. Most XUASTC LDR options also work in ASTC LDR mode.
- To compress an LDR sRGB image to an ETC1S .KTX2 file, at quality level 100 (the highest):