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feat: discard stale embedded page thumbnails when rewriting PDF

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A page may carry an optional /Thumb image XObject (ISO 32000-2 12.3.4),
a miniature rendering used only as a navigation aid. OCRmyPDF alters
page appearance (deskew, clean, rasterize, re-render) and plugins may
edit pages arbitrarily, so a retained thumbnail would be stale and no
longer match its page. Modern viewers generate thumbnails on demand, so
there is no loss of functionality.

OcrGrafter.finalize() now strips /Thumb from every page before saving,
alongside the existing search-index discard, covering both the OCR and
hOCR pipelines. Orphaned thumbnail XObjects are garbage-collected on save.
This commit is contained in:
James R. Barlow
2026-06-07 00:30:34 -07:00
parent 015b53ae30
commit 8f2bcc2c64
3 changed files with 126 additions and 0 deletions
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docs/releasenotes/version17.md
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@@ -13,6 +13,12 @@
would leave a stale index that returns incorrect search results in Acrobat.
Modern viewers rebuild a search index on demand, so there is no loss of
search capability.
- OCRmyPDF now discards embedded per-page thumbnail images (the optional
``/Thumb`` image XObject on a page) from its output. OCRmyPDF alters page
appearance (deskew, clean, rasterize, re-render) and plugins may edit pages
arbitrarily, so a retained thumbnail would be stale and no longer match its
page. Embedded thumbnails are a navigation aid that modern viewers generate
on demand, so there is no loss of functionality.
- Fixed a regression in OCR quality for PDFs that paint a 1-bit image mask
(stencil) with a gray or colored fill color. Previously such pages were
rasterized as 1-bit black-and-white before OCR, so Ghostscript dithered