PicoWebP

Fixed

• Cap VP8 chroma DC quantisation at 132 so low-quality output matches the encoder's reconstruction and the decoder's prediction state.
• Preserve adapted coefficient probabilities across exportState() / importState(), keeping resumed output byte-identical to single-shot encoding.
• Decode separate and reordered baseline JPEG scans into the correct component planes, with one block per MCU for single-component scans.
• Reset PNG transparency keys and JPEG ICC, Adobe colour-transform, and restart settings when a reader instance decodes another image.
• Make the CLI default to its advertised quality 80, honour --alpha=fail for raw alpha planes, and return exit code 1 for invalid reader or encoder input.
• Report explicitly selected alpha filters correctly and reject invalid filter values, empty alpha dimensions, invalid VP8 dimensions, and RGB buffer lengths.
• Remove a PHP 8.1+ float-to-integer deprecation from the test fixture and correct stale encoder comments. Add regression coverage for the fixes, including libwebp reconstruction checks and optional cjpeg scan fixtures.

First release. picowebp writes VP8 lossy WebP key frames in pure PHP — no GD, no Imagick, no cwebp, no libwebp, no shelling out — for the host that has no WebP support at all.

Added

Encoder

• PicoWebP\Vp8\Vp8LossyEncoder — takes a packed RGB string and returns a complete WebP file. fromQuality() / qIndexForQuality() map a 0–100 quality onto the VP8 quantiser.
• 16×16 and 4×4 intra prediction (all ten B_PRED modes) under a rate-distortion mode search, coefficient-probability adaptation, macroblock skip flags, and an optional per-coefficient trellis pass — off by default, because it buys ~14% fewer bytes at ~2.8 dB of PSNR on a real photograph.
• CPU/bytes knobs at both the API and the CLI: enableRd, rdLambda, rdPruneCandidates, adaptProbs, enableBPred, enableSkipFlags, enableTrellis, and the --no-rd, --no-adapt-probs, --prune, --trellis, --no-skip flags that go with them.

Container features

• Alpha: a translucent source is written as VP8X + ALPH + VP8 , with the alpha plane coded losslessly and byte-exactly; fully opaque images keep the simple VP8 container. --alpha=keep|flatten|fail, --alpha-filter=0..3.
• Colour profiles: PNG iCCP and JPEG APP2 profiles are carried through to an ICCP chunk. --icc=FILE, --no-icc.

Bundled readers — pure PHP, no image extension required

• PngReader — every colour type and bit depth, interlaced or not, palettes and tRNS, iCCP. Palette images are expanded to true colour before anything reads a pixel, and all eight bits of alpha are kept where libgd rounds to seven.
• JpegReader — baseline sequential 8-bit JPEG, greyscale or YCbCr, every sampling factor, restart markers, APP2 ICC.
• ImageInput — one entry point over both, plus GD where GD happens to be installed: pixels(), load(), isWebp(), mayHaveAlpha(), iccProfile(), and the $preferBundled / $gdAvailable switches.

An input that is already a WebP

• ImageMeta sniffs RIFF....WEBP on the file's bytes, not its extension, and reports real geometry for the VP8X, VP8 and VP8L containers.
• ImageInput::pixels() throws SkippedInput — a RuntimeException, so a caller that has never heard of it keeps working — carrying reason(), slug() and meta. --reencode-webp overrides it, and that path needs GD.

Command line

• bin/picowebp in.jpg out.webp, with --rgb=WxH and --alpha-plane=FILE for headerless input, --dump-yuv=FILE, --json, --bundled, --no-gd, --reencode-webp.
• Exit codes a queue can act on: 0 encoded, 1 error, 3 --alpha=fail refused, 4 skipped. A destination that cannot be written — a missing directory, a directory, an unwritable --dump-yuv path — is a failure with a message rather than a save that never happened.

Resumable path

• PlaneStore decodes once and stages the padded planes to disk; the encoder then works in bands of macroblock rows — beginBand(), encodeRowRange(), compactReconWindow(), finishFrame() — with exportState() / importState() carrying a part-done frame across invocations. Output is byte-identical to the single-shot encoder. It costs about twice the CPU and buys memory headroom and resumability, not speed.

Everything else

• PicoWebP\Spike\Vp8lEncoder, the internal lossless helper that supplies the headerless stream an ALPH chunk needs. Not a general-purpose lossless encoder, and not a PNG replacement.
• examples/encode.php and examples/chunked-queue.php.
• php tests/run.php (also composer test): bitstream structure, the alpha and ICC containers, PSNR against the source when dwebp is on PATH, both the bundled readers and the GD path, the WebP-skip route end to end, and the CLI's failure exit codes.

Notes

• Requires PHP 8.1+ and ext-zlib. ext-gd is optional: it is faster where it exists, and it is the only route to a progressive JPEG or to re-encoding a WebP source.
• Progressive JPEG is not decoded without GD. The bundled reader refuses it by name, saying which variant it found, rather than guessing.
• BMP, GIF, TIFF/TIF and raw Y′CbCr inputs are not implemented.
• This is a fallback encoder, not a libwebp replacement. Expect roughly 200–300× libwebp's CPU, a 377 s / 84 MB queue job for one 12 MP frame, and up to 21% larger files on flat logos and UI artwork. The measured tables, and what would move them, are in the README.