openpdf-renderer: honor /SMask soft masks on Image XObjects - #1604
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openpdf-renderer: honor /SMask soft masks on Image XObjects#1604andreasrosdalw wants to merge 2 commits into
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Image XObjects with a /SMask entry (PDF §11.6.5.3) -- the mechanism behind transparent-background PNGs (logos, product photos, ...) embedded in a PDF -- previously rendered fully opaque, since decodeImage()/renderImage() never looked at /SMask. Decode the soft mask as an 8-bit DeviceGray alpha channel (supporting the same JPEG/JPX/Flate/uncompressed encodings as the base image raster path, with nearest-neighbor resampling when the mask's own dimensions differ from the base image's) and composite it onto the decoded image before drawing. Update the README to document the new capability.
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| Metric | Results |
|---|---|
| Complexity | 7 |
| Duplication | 0 |
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Consolidated into LibrePDF#1607 along with the README updates for LibrePDF#1604, LibrePDF#1605, and LibrePDF#1606, so these four independent PRs (all based on master) don't each carry their own overlapping README.md diff and risk merge conflicts with each other depending on merge order.
Consolidated into LibrePDF#1607 along with the README updates for LibrePDF#1603, LibrePDF#1605, and LibrePDF#1606, so these four independent PRs (all based on master) don't each carry their own overlapping README.md diff and risk merge conflicts with each other depending on merge order.
andreasrosdalw
added a commit
to andreasrosdalw/OpenPDF
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Jul 28, 2026
Consolidated into LibrePDF#1607 along with the README updates for LibrePDF#1603, LibrePDF#1604, and LibrePDF#1606, so these four independent PRs (all based on master) don't each carry their own overlapping README.md diff and risk merge conflicts with each other depending on merge order.
andreasrosdalw
added a commit
to andreasrosdalw/OpenPDF
that referenced
this pull request
Jul 28, 2026
Consolidated into LibrePDF#1607 along with the README updates for LibrePDF#1603, LibrePDF#1604, and LibrePDF#1605, so these four independent PRs (all based on master) don't each carry their own overlapping README.md diff and risk merge conflicts with each other depending on merge order.
This was referenced Jul 28, 2026
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Summary
OpenPdfCorePageRenderer.decodeImage()/renderImage()never looked at an Image XObject's/SMaskentry (PDF §11.6.5.3 soft mask), so images were always painted fully opaque./SMaskis exactly how a transparent-background PNG (a logo, a product photo, a watermark, ...) ends up embedded in a PDF, so this was a real, common visual bug: such images rendered as a solid opaque rectangle instead of blending into the page.applySoftMask/compositeSoftMaskresolve the (possibly indirect)/SMaskstream, decode it as an 8-bit DeviceGray alpha channel viareadSoftMaskGray(supporting JPEG/JPX viaImageIO, Flate-decoded, and uncompressed encodings — the same set already supported for base image rasters), and composite it onto the decoded base image, producing aTYPE_INT_ARGBresult. The soft mask's own/Width//Heightneed not match the base image (legal per spec) — handled with nearest-neighbor resampling./Mask(stencil / color-key masking) is not yet handled.openpdf-renderer/README.md's XObject-coverage section to document the new capability.