16-bit lossy VarDCT for RGB/RGBA#84
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Lossy VarDCT previously accepted only 8-bit RGB/RGBA and silently fell back to lossless Modular for 16-bit input, even though the lossless Modular path has supported 8- and 16-bit since v1.0. This closes that gap: - VarDCTEncoder.forward accepts .uint16 frames; srgb8ToLinear generalises to srgbToLinear(_:maxValue:), keeping the 8-bit pixel loop byte-for-byte unchanged (no per-pixel branch on the default hot path) and adding a separate 16-bit loop. - VarDCTBitstreamWriter threads the real bit depth into ImageMetadata/ExtraChannelInfo instead of hardcoding 8, and fixes a latent alpha-unpack stride bug (frame.data[i*ch+3] only gave the right byte for 1-byte samples) that would have corrupted 16-bit RGBA alpha. encodeAnimation now rejects frames that disagree on bit depth rather than silently misdeclaring the shared metadata. - JXLDecoder's VarDCT reconstruction reads metadata.bitDepth and emits a uint16 ImageFrame when appropriate, mirroring the pattern the Modular path already used in assembleImageFrame. Verified via the djxl 0.11.2 oracle (16-bit RGB/RGBA/multi-group bitstreams decode within max-diff 3-16/65535 of our own decoder; alpha bit-exact) and a byte-for-byte regression diff against a pre-change build (8-bit lossy, 8/16-bit lossless, and multi-frame animation all byte-identical — zero drift on the existing default path). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Bump JXLToolVersion 1.2.0 -> 1.3.0, Package.swift status, CLAUDE.md's implementation-status table, and add the CHANGELOG 1.3.0 entry. Highlights (full notes in CHANGELOG.md): - Lossy VarDCT now accepts 16-bit RGB/RGBA (previously 8-bit only), matching the lossless Modular path's bit-depth range. Existing 8-bit lossy and all lossless output is byte-for-byte unchanged. - Fixes a latent 16-bit RGBA alpha-channel corruption bug in the VarDCT bitstream writer's alpha-unpack stride. Verified via reference libjxl 0.11.2 (djxl accepts every generated 16-bit bitstream; our decoder agrees with djxl within a few LSBs) and a byte-for-byte regression diff against a pre-change build. The full XCTest suite needs an Xcode host (this dev env has only CommandLineTools); the djxl spec gate was exercised via CLI round-trips, and the new tests' logic was additionally verified through a throwaway executable target linked against the built library (removed before this commit). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
VarDCTEncoder,VarDCTBitstreamWriter, andJXLDecodernow handle 16-bit RGB/RGBA end-to-end.VarDCTBitstreamWriter.buildFrameSectionsused a byte stride only correct for 8-bit samples, which would have corrupted 16-bit RGBA alpha.encodeAnimationnow rejects frames that disagree on bit depth instead of silently misdeclaring the sharedImageMetadata.JXLToolVersion,Package.swift/CLAUDE.mdstatus).Test plan
swift build -c releasecleanswift test -c releaserun on an Xcode host to close the loop🤖 Generated with Claude Code