v1.2.0: public reverse JPEG recompression + YCoCg-R lossless RCT#83
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Add `public JXLDecoder.decodeLosslessJPEG(_:)` — the symmetric mirror of the existing public `encodeLosslessJPEG(_:)`. It chains the previously package-only reverse pipeline (parseJXLContainer -> extractJBRDBox -> JBRDBoxReader -> BrotliDecoder -> decodeJPEGBridgeData -> JXLToJPEGAdapter.reconstruct) so an external `import JXLSwift` consumer can reconstruct the byte-identical original JPEG. The adapter/bridge types stay `package`; only the one wrapper becomes public. - Refactor `jxl-tool transcode --mode reverse` into a thin client over the new public API (extract transcodeJXLtoJPEGFromSource / writeReverseOutput; keep the optional --source fallback). - Add `async` overloads for the recompression pair (encodeLosslessJPEG / decodeLosslessJPEG) to complete the J2KSwift async-facade parity. - Add PublicAPILosslessJPEGTests using a plain `import JXLSwift` (NOT @testable) so compilation alone pins external reachability, plus a forward -> reverse byte-identical round trip and a fail-safe negative case. Validated end-to-end through the built `jxl` binary: forward bridge -> reverse is byte-identical for 4:4:4 / 4:2:0 / 4:2:2 / grayscale; a JXL with no jbrd box is refused (no wrong bytes). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
…p), cost-gated Apply the reversible YCoCg-R colour transform to RGB/RGBA channels before prediction in SpecModularEncoder, decorrelating R,G,B -> Y,Co,Cg so the chroma channels compress to near-nothing. `RCT.forwardPixel(.ycocgR)` is the exact inverse of the decoder's `SpecRCT.inverse(rctType: 6)`. The transform descriptor is emitted only in the section-0 / DC-global GroupHeader of every single- and multi-group candidate (baseline / activity-split / greedy); per-AC-group headers stay empty, so the decoder inverts on the assembled image (libjxl-canonical — transforms live in the global modular header). - Drop the redundant `[0, sampleHi]` clamp on the gradient predictor in the modular residual paths: a no-op for in-range data (existing byte-exact output is unchanged) but it diverged from the decoder's ClampedGradient (applyLibjxlPredictor id 5) for RCT's signed / over-range Co/Cg, which would have broken the round trip. - Cost-gate RCT (estimateGradientResidualBits): apply YCoCg-R only when its estimated residual bit-cost beats the raw R,G,B estimate, so RCT can never inflate a frame (already-decorrelated / independent-channel content keeps the identity path). - Add the testRCT_LosslessRGB_DecorrelatesIdenticalChannels regression guard (R=G=B => Co=Cg=0 => RGB ~ grayscale, not 3x) to catch a silent RCT-disable. Self-round-trip validated pixel-exact across single- and multi-group, 8/16-bit RGB/RGBA, efforts 3/7/9, correlated + adversarial random, grayscale no-regression. A/B vs a no-RCT build: 21-66% smaller on correlated content, equal on independent content. NOTE: the djxl byte-exact cross-validation (RobustnessTests DjxlSubset / ConformanceTests) must be run on a host with djxl + XCTest; it could not be run in the dev env where this was authored. The change is high-confidence (the decoder's RCT is already djxl-validated against cjxl RGB output) but should be confirmed before merge. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Bump JXLToolVersion 1.1.0 -> 1.2.0, Package.swift status, and add the CHANGELOG 1.2.0 entry. Highlights (full notes in CHANGELOG.md): - Public `JXLDecoder.decodeLosslessJPEG(_:)` — reverse JPEG recompression, the mirror of `encodeLosslessJPEG`; `jxl transcode --mode reverse` is now a thin client over it. Plus async overloads for the recompression pair. - Lossless RGB/RGBA YCoCg-R RCT (single + multi-group), cost-gated: 21-66 % smaller on correlated content, never inflates, decode unchanged. Verified via reference libjxl 0.11.2: RCT output djxl-byte-exact across single/multi-group 8/16-bit RGB/RGBA; JPEG recompression byte-identical both directions (cjxl->our reverse, our forward->djxl). The full XCTest suite needs an Xcode host (the dev env has only CommandLineTools); the djxl spec gate was exercised directly through the CLI. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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v1.2.0 — public reverse JPEG recompression + YCoCg-R lossless RCT
Completes JPEG-XL transfer-syntax exposure and adds a lossless ratio win.
Reverse JPEG recompression (public API)
public JXLDecoder.decodeLosslessJPEG(_:) throws -> Data— the symmetric mirror ofencodeLosslessJPEG; reconstructs the byte-identical original JPEG from a JPEG-bridge JXL. Adapter/bridge types staypackage.jxl transcode --mode reverserefactored into a thin client over it (kept the--sourcefallback).asyncoverloads for the recompression pair (J2KSwift facade parity).PublicAPILosslessJPEGTests(plainimport JXLSwift, not@testable) pins external reachability + a fail-safe negative case.Lossless YCoCg-R RCT — RGB/RGBA, single + multi-group
[0,sampleHi]gradient-predictor clamp in the residual paths (a no-op in-range; required so RCT's signed/over-range chroma round-trips).testRCT_LosslessRGB_DecorrelatesIdenticalChannelsregression guard.Verification (reference libjxl 0.11.2, via CLI)
jxl encode -l→djxldecode → original pixels byte-exact across single/multi-group, 8/16-bit RGB/RGBA, correlated + random.cjxl --lossless_jpeg=1→ ourdecodeLosslessJPEG→ byte-identical, and our forward bridge →djxl→ byte-identical (4:4:4 / 4:2:2 / 4:2:0 / grayscale).swift build -c releaseclean.🤖 Generated with Claude Code