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OCR/openspec/changes/archive/2025-12-11-unify-direct-track-pdf-rendering/proposal.md
egg 24253ac15e feat: unify Direct Track PDF rendering and simplify export options 
Backend changes:
- Apply background image + invisible text layer to all Direct Track PDFs
- Add CHART to regions_to_avoid for text extraction
- Improve visual fidelity for native PDFs and Office documents

Frontend changes:
- Remove JSON, UnifiedDocument, Markdown download buttons
- Simplify to 2-column layout with only Layout PDF and Reflow PDF
- Remove translation JSON download and Layout PDF option
- Keep only Reflow PDF for translated document downloads
- Clean up unused imports (FileJson, Database, FileOutput)

Archives two OpenSpec proposals:
- unify-direct-track-pdf-rendering
- simplify-frontend-export-options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
2025-12-12 07:50:43 +08:00

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Change: Unify Direct Track PDF Rendering with Background Image + Invisible Text Layer

Why

Direct Track PDF generation currently has visual rendering issues:

  1. Chart text overlap: Text elements extracted from PDF text layer (e.g., "Temperature, °C") overlap with chart images
  2. Z-order problems: White text on dark backgrounds becomes invisible when rendered incorrectly
  3. Office document issues: PPT/DOC/XLS converted PDFs lose visual fidelity (vector graphics, gradients)

The root cause is that Direct Track tries to render individual elements (text, images, tables) separately, which leads to z-order conflicts and missing visual content.

What Changes

Backend Changes

  1. Unified Background Image Rendering for All Direct Track

    • Render source PDF page as full-page background image (2x resolution)
    • Draw invisible text layer on top (PDF Text Rendering Mode 3)
    • Text remains searchable/extractable but doesn't visually overlap

  2. Chart Region Exclusion

    • Add CHART element type to regions_to_avoid
    • Chart-internal text (axis labels, legends) will NOT be in invisible text layer
    • These texts are already visible in the background image and don't need translation

  3. Skip Element Rendering When Background Exists

    • When background image is rendered, skip individual image/table rendering
    • Only draw invisible text layer for searchability and translation extraction

Frontend Considerations

  1. No UI Changes Required for Layout PDF

    • Layout PDF generation is automatic, no user options needed
    • Visual output will match source PDF exactly

  2. Translation Flow Clarification

    • Layout PDF: Background image + invisible text (for preview)
    • Translated PDF: Reflow layout with real visible text (page-by-page)
    • Chart text excluded from translation (already in background image)

Impact

  • Affected specs: document-processing, result-export, translation
  • Affected code:
    • backend/app/services/pdf_generator_service.py (main changes)
    • backend/app/services/direct_extraction_engine.py (chart detection)
  • File size: Output PDF will be larger due to embedded page images (~2MB per page at 2x resolution)
  • Processing time: Slight increase for page rendering

Migration

  • No database changes required
  • No API changes required
  • Existing tasks can be re-exported with new PDF generation logic