jedarden e8992816ce docs(pdftract-25k4x): verify figure and caption detection implementation

Add verification note confirming all acceptance criteria PASS.
- Figure classifier: 16/16 tests pass
- Caption classifier: 8/8 tests pass
- All acceptance criteria verified against code

Closes pdftract-25k4x

2026-06-01 10:55:56 -04:00

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Figure and Caption Detection Verification - pdftract-25k4x

Acceptance Criteria Verification

1. Image XObject, no text overlap: 1 Figure block

Location: crates/pdftract-core/src/layout/figure.rs:130

Checks text_overlap_area / image_area < 0.5
Creates Block with kind="figure"
PASS - Tests: test_classify_figure_pure_visual_image, test_classify_figure_no_glyphs

2. Image + small-font caption 1 line below: Figure + Caption

Location: crates/pdftract-core/src/layout/caption.rs:126-140

Checks block.median_font_size < ctx.page_body_median (small font)
Checks vertical_distance < 2.0 * ctx.line_height (within 2 lines)
Sets kind to "caption"
PASS - Test: test_caption_immediately_below_figure

3. Image overlapping text (background): NOT Figure

Location: crates/pdftract-core/src/layout/figure.rs:130

Images with >= 50% text overlap are NOT classified as figures
PASS - Tests: test_classify_figure_text_on_image, test_classify_figure_partial_text_above_threshold

4. Caption 5 lines below: NOT Caption

Location: crates/pdftract-core/src/layout/caption.rs:145-148

Checks vertical_distance >= 2.0 * ctx.line_height
Returns false if too far below
PASS - Test: test_caption_too_far_below_figure

5. Caption different column: NOT Caption

Location: crates/pdftract-core/src/layout/caption.rs:152-154

Checks block.column != figure.column in multi-column layouts
Returns false if different column
PASS - Test: test_caption_different_column

Test Results

Figure Classifier Tests (16/16 PASS)

test_bboxes_intersect
test_classify_figure_no_images
test_classify_figure_partial_text_below_threshold
test_classify_figure_partial_text_above_threshold
test_classify_figure_exactly_at_threshold
test_classify_figure_no_glyphs
test_classify_figure_pure_visual_image
test_bbox_area
test_classify_figure_sort_order
test_classify_figure_empty_context
test_classify_figure_text_on_image
test_compute_text_overlap_area_multiple_glyphs
test_compute_text_overlap_area_union
test_figure_block_properties
test_five_figures_no_text
test_text_covered_image_not_figure

Caption Classifier Tests (8/8 PASS)

test_caption_above_figure
test_caption_font_not_smaller
test_caption_too_far_below_figure
test_no_previous_figure
test_caption_different_column
test_caption_immediately_below_figure
test_block_accessors
test_page_classification

INV Verification

INV: Figure block has empty lines Vec - SATISFIED: Block created with text=String::empty(), median_font_size=0.0
Caption above figure NOT detected in v0.1.0 - SATISFIED: caption.rs test_caption_above_figure returns false

Files Verified

crates/pdftract-core/src/layout/figure.rs (517 lines)
crates/pdftract-core/src/layout/caption.rs (342 lines)
crates/pdftract-core/src/layout/mod.rs (exports classifiers)

Verification Status

ALL ACCEPTANCE CRITERIA PASS - Implementation complete and tested.

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