Editing S3 Texture Compression (section)

== Further variants ==

=== BC4 and BC5 ===
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BC4 and BC5 (Block Compression 4 and 5) are added in Direct3D 10. They reuse the alpha channel encoding found in DXT4/5 (BC3).<ref name="reed">{{cite web |last1=Reed |first1=Nathan |title=Understanding BCn Texture Compression Formats |url=http://www.reedbeta.com/blog/understanding-bcn-texture-compression-formats/ |website=Nathan Reed’s coding blog |access-date=2020-09-01 |archive-date=2020-11-09 |archive-url=https://web.archive.org/web/20201109040712/http://www.reedbeta.com/blog/understanding-bcn-texture-compression-formats/ |url-status=live }}</ref>
* BC4 stores 16 input single-channel (e.g. greyscale) pixels into 64 bits of output, encoded in nearly<ref name=ryg/> the same way as BC3 alphas. The expanded palette provides higher quality.
* BC5 stores 16 input double-channel (e.g. tangent space normal map) pixels into 128 bits of output, consisting of two halves each encoded like BC4.

=== BC6H and BC7 ===
BC6H (sometimes BC6) and BC7 (Block Compression 6H and 7) are added in Direct3D 11.<ref name="reed"/>
* BC6H encodes 16 input RGB HDR (float16) pixels into 128 bits of output. It essentially treats float16 as 16 sign-magnitude integer value and interpolates such integers linearly. It works well for blocks without sign changes. A total of 14 modes are defined, though most differ minimally: only two prediction modes are really used.<ref name=ryg>{{cite web |last1=Giesen |first1=Fabian “ryg” |title=GPU BCn decoding |url=https://fgiesen.wordpress.com/2021/10/04/gpu-bcn-decoding/ |website=The ryg blog |access-date=24 July 2023 |language=en |date=4 October 2021 |archive-date=24 July 2023 |archive-url=https://web.archive.org/web/20230724085332/https://fgiesen.wordpress.com/2021/10/04/gpu-bcn-decoding/ |url-status=live }}</ref>
* BC7 encodes 16 input RGB8/RGBA8 pixels into 128 bits of output. It can be understood as a much-enhanced BC3.<ref name=ryg/>

BC6H and BC7 have a much more complex algorithm with a selection of encoding modes. The quality is much better as a result.<ref name="reed"/> These two modes are also specified much more exactly, with ranges of accepted deviation. Earlier BCn modes decode slightly differently among GPU vendors.<ref name=ryg/>