Editing S3 Texture Compression (section)

=== 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.