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pdf-inspector/tests/fixtures/text_page_with_watermark_image.pdf
371de80b14 fix: extract_pages_markdown's needs_ocr now agrees with classify_pdf (#231)
* fix: extract_pages_markdown's needs_ocr now agrees with classify_pdf

Fixes #227.

extract_pages_markdown_mem computed its per-page needs_ocr entirely
from text-quality signals: decoding/garble issues, empty markdown, GID
fonts, garbage-text ratio. It had no awareness of the page's image
content at all — so a page that is fundamentally a full-page scan
with a little genuine native text drawn over it (a header, a stamp, a
cover-sheet annotation) extracts that text cleanly, trips none of the
text-quality checks, and reports needs_ocr=false — while
classify_pdf/detect_pdf_type correctly see the dominant background
image and flag the same page as needing OCR. Two public APIs
answering the same question, silently disagreeing, in the unsafe
direction (skipping OCR on a page that needs it).

Exposed detector::analyze_page_images at crate visibility (was
private) and call it per page in extract_pages_markdown_mem's loop —
the same "large background image" signal (>50% page coverage) that
already powers has_template_image in classify_pdf/detect_pdf_type,
rather than reimplementing image-area detection a second time with
its own thresholds that could drift out of sync again. When it's
true, the page is flagged needs_ocr (with OCR_REASON_SCANNED added
to ocr_reasons_by_page, matching how the same signal is already
reported elsewhere) and its markdown is blanked, exactly like the
existing text-quality-triggered needs_ocr paths already do — no
special-casing added for "cleanly-extracted-but-still-a-scan" text.

Verified against the issue's exact repro (a full-page raster with one
native text line drawn over it, built via reportlab/pillow): before
this fix, extract_pages_markdown_bytes reported page 0
needs_ocr=False with the header line as markdown while
classify_pdf_bytes correctly flagged pages_needing_ocr=[0]; after,
both agree needs_ocr=True and the page's markdown is empty. Confirmed
no regression on a normal text-based fixture (nexo-price-en.pdf:
needs_ocr stays False, full markdown returned). New Rust regression
test added exercising both APIs against the same fixture.

Full suite (860 tests, 1 new) passes; cargo clippy --all-targets
-- -D warnings unchanged at 28 pre-existing/unrelated errors.

* fix: gate has_template_image behind the same OCR signals classify_pdf uses

extract_pages_markdown_mem was treating has_template_image alone as
sufficient to force needs_ocr=true and discard the page's markdown, but
classify_pdf/detect_pdf_type never treats that raw signal alone as
needing OCR. A text page with a full-bleed watermark, letterhead, or
large figure would get its clean markdown wrongly blanked and routed
to OCR.

Added page_template_image_needs_ocr(), mirroring the two distinct
signals classify_pdf actually uses to decide a template-image page
needs OCR: the looks_like_scan gate (image_count <= 1, few text ops,
low alphanumeric diversity) used for Mixed-type routing, and the
insufficient-text-volume signal (text_operator_count < 10) that routes
a page with a dominant background image and only a couple of native
text calls to PdfType::ImageBased independent of looks_like_scan.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix: match per-page OCR threshold and add missing vector-text signal

Two follow-up findings on the has_template_image gate added in the
previous commit:

1. insufficient_text used a hard-coded threshold of 10 text operators,
   but Mixed-type per-page routing (the actual per-page decision this
   function tries to agree with) uses config.min_text_ops_per_page
   (default 3). The higher 10 threshold was borrowed from a *different*
   classify_pdf code path — the effective_min_ops floor used only for
   whole-document ImageBased/Scanned classification, a cross-page
   aggregate this per-page function can't replicate anyway. Using the
   lower per-page threshold removes a real disagreement window
   (3-9 text ops with high alphanumeric diversity) without breaking
   the #227 regression fixture (text_ops=1, still well under 3).

2. extract_pages_markdown_mem never checked has_vector_text at all,
   even though Mixed-type per-page routing always sends
   vector-outlined-text pages to OCR (outlined glyphs can't be
   extracted as text). A page with massive path ops plus a short
   genuine caption could extract that caption cleanly, slipping past
   the existing empty/garbage-text checks. Added
   page_has_vector_text() and wired it into needs_ocr the same way
   has_template_image is.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* perf: compute template-image and vector-text OCR signals in one pass

page_template_image_needs_ocr and page_has_vector_text each called
analyze_page_content independently, so every requested page's content
streams (page + XObjects) and image coverage were decompressed and
scanned twice per page with one result discarded each time.
detect_from_document avoids this by caching its per-page PageAnalysis;
extract_pages_markdown_mem had no such cache.

Merged both into page_ocr_signals(), a single analyze_page_content
call returning both signals as a tuple.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: Abimael Martell <1450169+abimaelmartell@users.noreply.github.com>
2026-08-05 15:41:44 -07:00

5.6 KiB