Richard Geldreich's Blog: XUBC7 Low-Level Format Document

A new codec called XUBC7 v1 is described as the first DCT-based BC7 texture compression codec. It supports lossless or lossy coding of the full BC7 format including all modes, partitions, and options, using absolute or residual DCT with dozens of predictors similar to modern image codecs like WebP. It offers threaded, all-integer deterministic decompression with optional SIMD, making it suitable for WASM. Lossless bitrate runs ~3.5-5.6 bpp and lossy ~1.2-2.5 bpp, compared to plain BC7's 8.0 bpp, with lossless mode rivaling lossy RDO BC7+LZ codecs in efficiency without quality loss. A planned v2 will use adaptive 2x2-4x4 macroblocks to push lossy bitrate below 1.0 bpp. The format is also described as universal, capable of transcoding the BC7 latent directly to ASTC LDR 4x4 blocks, falling back to a real-time analytical encoder (bc7f) for partition patterns that don't map directly.

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