pdftract/notes/pdftract-nf172.md

pdftract-nf172: Phase 3.5 Inline Image skip (coordinator)

Summary

Coordinator bead for Phase 3.5: detect and skip BI/ID/EI inline image sequences in content streams. All 3 children have been completed and the inline image parsing functionality is fully implemented.

Children Completed

All 3 children are CLOSED:

• pdftract-1sxpa: BI/ID inline image header parser - CLOSED (commit 4ac8479)
• pdftract-1f0cj: ID-to-EI raw-bytes scanner with whitespace-preceded EI detection - CLOSED
• pdftract-axcri: Inline image -> ImageXObject record in page image list - CLOSED

Acceptance Criteria Verification

Criterion	Status	Evidence
All 3 children closed	PASS	bf show confirms all 3 children are closed
Inline image followed by text operators parsed correctly	PASS	parse_inline_image() in render.rs advances lexer past EI; subsequent tokens parse normally
Embedded "EI" bytes not treated as terminator	PASS	Test test_scan_inline_image_data_with_embedded_ei passes - input b"ABCDEI\nEI" correctly returns b"ABCDEI" (inner EI not preceded by ws)

Implementation Overview

The inline image implementation works as follows:

1. Header parsing (pdftract-1sxpa): parse_inline_image_header() parses BI...ID dictionary with shorthand key expansion
2. Data scanning (pdftract-1f0cj): scan_inline_image_data() byte-by-byte scan for whitespace-preceded EI
3. ImageXObject recording (pdftract-axcri): collect_image_xobjects() records both XObject and inline images with CTM-derived bbox

Test Results

All 14 inline_image tests pass:

• test_scan_inline_image_data_basic - Basic BI...ID...EI parsing
• test_scan_inline_image_data_with_embedded_ei - EI in data not preceded by ws
• test_scan_inline_image_data_empty - Empty image
• test_scan_inline_image_data_no_ei - No terminator handling
• test_scan_inline_image_data_various_whitespace - All 6 ws bytes before EI
• test_scan_inline_image_data_binary_content - Binary data with 0x45/0x49 bytes
• test_scan_inline_image_data_lexer_position - Lexer advancement verification
• test_parse_basic_header - Basic header parsing
• test_shorthand_expansion - Shorthand key expansion
• test_id_whitespace_validation - ID whitespace requirement
• test_parse_header_with_array_filter - Array filter chains
• test_parse_header_with_missing_value - Malformed header recovery
• test_inline_image_header_new - Header construction
• test_inline_image_header_has_required_fields - Field presence

Integration with Content Stream Parser

The collect_image_xobjects() function in render.rs integrates inline image parsing into the content stream interpreter:

• BI keyword triggers parse_inline_image() which consumes the entire BI/ID/EI sequence
• Lexer is positioned after EI, allowing subsequent text operators to parse correctly
• ImageXObject entries are added to page image list for Phase 4.4 figure detection

Known Limitations

Per the plan's "Critical considerations":

• The whitespace-EI heuristic may terminate early if compressed image data contains <ws>EI (rare)
• A more robust solution would compute expected byte length from width/height/bpc/colorspace (deferred to v0.2.0+)

References

• Plan section: Phase 3.5 Inline Images (lines 1592-1600)
• ISO 32000-1 sec 8.9.7