When Tesseract reports a page with many diacritics, OCRmyPDF rewrites the
message to "lots of diacritics - possibly poor OCR", which hid the
original wording. Keep the interpreted hint but also emit Tesseract's raw
line at debug verbosity (-v 1) so users can see exactly what Tesseract
reported.
Closes#1566.
Ghostscript 10.x renders aliased glyphs that OCR frequently misreads as
extra word breaks or substituted characters. Enable text and graphics
anti-aliasing (-dTextAlphaBits=4 -dGraphicsAlphaBits=4) for the contone
raster devices, which empirically improves OCR accuracy on the
Ghostscript path, especially for small fonts at moderate DPI. The 1-bit
mono devices are excluded, since older Ghostscript rejects alpha bits on
them and pngmonod performs its own anti-aliased downscaling.
Also log which rasterizer rendered each page at debug verbosity and
clarify the --rasterizer help text, so quality reports are easier to
diagnose. The default rasterizer (auto) already prefers pypdfium2, which
anti-aliases; this primarily benefits --rasterizer ghostscript and
installs without pypdfium2.
Closes#1439.
The optimizer is best-effort: any image it cannot process is left
unchanged in the output, which remains valid. Previously, an extraction
failure (e.g. an exotic colorspace pikepdf cannot transcode) was logged
with log.exception, printing a full traceback at ERROR level that alarmed
users even though nothing was wrong with the output (issue #846).
Trap such failures with a concise warning that the image was left
unchanged and the output is still valid, and demote the traceback to
debug verbosity for diagnosis.
Ghostscript's `auto` image compression heuristic can transcode lossless
images to JPEG during PDF/A generation, which is surprising at
optimization levels that otherwise promise lossless-only operations
(issue #1124).
`--pdfa-image-compression=auto` (the default) now coerces to lossless at
-O0 so Ghostscript will not transcode lossless images to JPEG. -O1 and
above continue to defer to Ghostscript's heuristic; -O1 (the default
level) is kept as a historical exception because coercing it to lossless
substantially bloats output. Users wanting guaranteed lossless image
handling can pass --pdfa-image-compression=lossless or use -O0.
Also make `lossless` pass existing JPEGs through unchanged
(-dPassThroughJPEGImages=true) instead of re-encoding them with a
lossless codec, which only inflates already-lossy data.
Validate and repair the page-boundary boxes (MediaBox, CropBox, TrimBox,
ArtBox, BleedBox) of input PDFs in triage(), following PDF 2.0:
- Coerce coordinates written in invalid exponential notation, stored by
qpdf/pikepdf as strings (#1398).
- Normalize rectangles whose corners are given in reversed order, which
previously crashed with NegativeDimensionError (#1526).
- Clamp a crop/trim/art/bleed box that extends outside the MediaBox to
their intersection, or discard it when the intersection is empty, which
previously produced a zero-height effective page some viewers rejected
(#1400).
When a box is discarded, clamped, or reinterpreted, a warning recommends
visual inspection of the output. pdfinfo box reading shares the same
coercion helper so PdfInfo no longer crashes on malformed boxes.
Supersedes PR #1691. Thanks @ajdlinux.
Closes#1398, #1526, #1400
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.
Adobe Acrobat can embed a proprietary full-text search index in the
document catalog at /Root/PieceInfo/SearchIndex. Only Acrobat reads it;
other viewers ignore it and search the text on the fly. Any change to a
PDF invalidates the index, so once OCRmyPDF rewrites the document the
retained index is stale and returns incorrect search results in Acrobat.
OcrGrafter.finalize() now discards it before saving (covering both the
OCR and hOCR pipelines), preserving any other PieceInfo owner data and
dropping an empty PieceInfo. Modern viewers rebuild a search index on
demand, so there is no loss of search capability.
The API previously clobbered PIL.Image.MAX_IMAGE_PIXELS unconditionally
on every call, so host applications (e.g. Paperless-NGX) that configured
the PIL limit before invoking ocrmypdf.ocr() saw their setting silently
overwritten with the 250 MP default. Make max_image_mpixels default to
None and only apply the override when the caller explicitly sets it.
The CLI default of 250 MP is unchanged.
Fixes#1665
James R. Barlow