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stet 0.2.1 — PDF/X CMYK rendering correctness

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@AndyCappDev AndyCappDev released this 10 May 03:46
· 127 commits to main since this release
v0.2.1
52a306d

[0.2.1] — 2026-05-09

Patch release focused on PDF/X CMYK rendering correctness against the
Ghent PDF Output Suite (GWG)
test corpus. Fixes a family of bugs where ICCBased / Lab / DeviceN
fills, images, and transparency groups didn't round-trip through the
document's /OutputIntents profile correctly, producing visible
"X" markers in calibration swatches that should render uniform.

This is an additive, non-breaking release. Downstream code does
not need to change. New public API on stet-graphics::IccCache and
a new rendering_intent: u8 field on stet-graphics::ImageParams
are documented below.

Highlights

  • GWG 13.3 — ICCBased RGB paints with /OP true no longer route
    into the custom-spot overprint path; per PDF 1.7 §11.7.4.5 they
    paint as if /OP were false.
  • GWG 16.1 — per-intent PDF/X proofing chain (source A2B → PCS → OI B2A → CMYK) is built for every registered ICCBased RGB
    profile, threaded through op_ri / ExtGState /RI.
  • GWG 16.4 — transparency groups with no /CS (inherit) now
    resolve correctly to the parent's CMYK compositing space when
    the parent is a /CS DeviceCMYK group.
  • GWG 17.2 — ICCBased images now go through the proofing chain
    via convert_image_8bit_with_intent (was bypassing the
    OutputIntent roundtrip and rendering via direct source→sRGB).
  • GWG 22.1 — Lab fills populate DeviceColor::native_cmyk via
    a direct Lab → PCS → OI B2A → CMYK chain (matches Adobe ACE),
    and the OutputIntent install path pre-warms the sRGB→CMYK
    reverse transform so the parallel CMYK buffer never falls back
    to the PLRM (1-r, 1-g, 1-b, 0) formula.
  • WASM viewer — open_pdf now applies the document's
    OutputIntent before storing the cached state, so PDF/X documents
    render in the browser the same way they do in the CLI.

Added — public API (additive, non-breaking)

stet-graphics:

  • IccCache::convert_to_oi_cmyk(hash, components, intent) — run an
    RGB ICC color through the proofing chain at the given intent and
    return the intermediate OutputIntent CMYK.
  • IccCache::convert_lab_to_oi_cmyk(l, a, b, intent) — direct
    Lab → OI CMYK via the OI's per-intent B2A LUT.
  • IccCache::convert_image_8bit_with_intent(hash, samples, pixel_count, intent) — bulk image conversion with explicit
    rendering intent.
  • IccCache::convert_color_with_intent and
    convert_color_readonly_with_intent — per-intent single-color
    conversion.
  • IccCache::prepare_lab_to_oi_cmyk() — pre-build per-intent
    Lab→OI samplers; pair with prepare_reverse_cmyk().
  • IccCache::intent_from_pdf_byte(b: u8) — map PDF rendering-intent
    bytes (0..3) to IccRenderingIntent.
  • pub use moxcms::RenderingIntent as IccRenderingIntent.
  • pub struct LabToCmykSampler (in icc::perceptual) with
    pub fn sample_pdf_lab(l, a, b).
  • New field ImageParams::rendering_intent: u8. Default is 0
    (Perceptual). Per the documented "be a reader, not a writer"
    policy for param structs (CLAUDE.md), this is additive and not
    treated as a SemVer break.

stet-pdf-reader:

  • PdfDocument::apply_output_intent_as_default_cmyk() now also
    pre-warms the sRGB→CMYK reverse and per-intent Lab→OI samplers
    in addition to its previous behaviour. No signature change.
  • Image XObjects with /Intent now propagate the per-image
    rendering intent into ImageParams.rendering_intent, overriding
    the gstate /RI per ISO 32000 §11.3.4.

stet-render:

  • build_icc_cache_for_list now also pre-warms the per-intent
    Lab→OI samplers when proofing is enabled.

Fixed

  • DeviceGray painted in a PDF/X DeviceCMYK page group now routes
    through the K plate (matches DeviceCMYK 0/0/0/(1−g) byte-for-byte).
  • DeviceN images with a non-CMYK alternate space go through the
    overprint path so process plates aren't disturbed.
  • Paired /OP true /op true ExtGStates are now treated as a
    "strict overprint" signal (matches Adobe Illustrator's emit).
  • The custom-spot overprint dispatch and the parallel CMYK buffer's
    is_custom_spot heuristic both now require
    process_cmyk.is_some() so proofing-chain ICCBased RGB stays out.

Verification

  • 11 GWG calibration tests pass: 13.0 / 13.3 / 16.1 / 16.4 / 17.2 /
    17.3 / 22.1 / 23.0 / 1.0 / 3.0 / 12.0 / 8.0.1.
  • cargo test --workspace --release clean.
  • cargo fmt --all -- --check clean. No new clippy errors.
  • wasm-pack build --target web --release crates/stet-wasm clean.

Crates published at 0.2.1

stet, stet-cli, stet-fonts, stet-graphics, stet-core,
stet-ops, stet-engine, stet-render, stet-viewer,
stet-pdf-reader, stet-pdf. The vendored stet-tiny-skia /
stet-tiny-skia-path forks remain at 0.11.4. stet-wasm is
excluded from crates.io and bumped to 0.1.1 independently.

Full changelog: v0.2.0...v0.2.1

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