# PDF layouts and OCR
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> You are in a sub-page of **Chunking**. > To reorient, go back here: > > - [**Chunking** — text segmentation and context window management](./README.md) > - [**WFGY Global Fix Map** — main Emergency Room, 300+ structured fixes](../README.md) > - [**WFGY Problem Map 1.0** — 16 reproducible failure modes](../../README.md) > > Think of this page as a desk within a ward. > If you need the full triage and all prescriptions, return to the Emergency Room lobby.
A practical pipeline to extract clean, ordered text with stable offsets from PDFs and scanned pages, so your chunks, citations, and typed blocks remain consistent across reindex runs. ## Open these first - Stable chunk ids: [chunk_id_schema.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/chunk_id_schema.md) - Title hierarchy and numbering: [title_hierarchy.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/title_hierarchy.md) - Section boundaries after titles: [section_detection.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/section_detection.md) - Code and tables as typed blocks: [code_tables_blocks.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/code_tables_blocks.md) - Safe reindex after small edits: [reindex_migration.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/reindex_migration.md) - Why this snippet and offsets: [retrieval-traceability.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/retrieval-traceability.md) - Payload contracts for RAG: [data-contracts.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/data-contracts.md) - Visual map of the whole RAG path: [rag-architecture-and-recovery.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/rag-architecture-and-recovery.md) ## Acceptance targets - Word error rate (WER) ≤ 0.025 on clean pages, character error rate ≤ 0.01 on headings and captions. - Header and footer removal: false positive rate ≤ 0.01, false negative rate ≤ 0.03 on a 30 page sample. - Reading order is monotonic by column. Cross column jumps never split a sentence. - Hyphenation merges correct ≥ 0.98 and never fire inside code or tables. - Captions attach to the correct figure or table in the same section. - Offsets remain stable across two reindex runs. Drift ≤ 0.5 percent of file length. - ΔS(question, retrieved) ≤ 0.45 on queries that cite a figure, table, or equation anchor. --- ## Pipeline overview 1) **Ingest with layout** Extract characters with bounding boxes, font name, size, bold/italic flags, page number, and line ids. For scans, run OCR first to obtain the same fields. 2) **Coordinate normalization** Normalize all positions to a unified page space. Keep `bbox = [x0, y0, x1, y1]` in points or millimeters. Record page width and height. 3) **Template detection for headers and footers** Build n-gram histograms by y bands across pages. Mark a header band if a repeating string appears on ≥ 60 percent of pages at near identical y. Do the same for footers and running titles. Remove matched runs before paragraph assembly. 4) **Column segmentation** Use whitespace cuts on the x axis. A stable valley between two dense x clusters marks a column boundary. For three columns, expect two valleys. Validate by line alignment and average line width. 5) **Line forming and paragraph assembly** Join characters into words, words into lines by y proximity and left margin continuity. Join lines into paragraphs when leading and trailing margins are stable and the interline gap is below a threshold for that page. 6) **Hyphenation repair** If a line ends with a hyphen and the next line begins with a lowercase letter or an alphanumeric continuation, and both are inside a prose paragraph, remove the hyphen and join. Never apply inside code or table blocks. Keep an exceptions list for chemical names and proper nouns. 7) **Typed block extraction** Detect code blocks, tables, figures, and captions, and lift them as first class blocks with offsets. See [code_tables_blocks.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/code_tables_blocks.md). 8) **Section alignment** Align blocks to sections detected from the title tree. See [title_hierarchy.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/title_hierarchy.md) and [section_detection.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/section_detection.md). 9) **Canonical text build** Emit a single canonical text with byte offsets for every block and section. Keep a map `{block_id → [off_begin, off_end], page, bbox}` for traceability. --- ## Header and footer detection Signals - Repetition across pages of the same string at nearly the same y. - Presence of page numbers, dates, running titles, or publisher marks. - Font size smaller than body text and high contrast with empty surroundings. Algorithm sketch - Slice the page into 32 horizontal bands. For each band, compute the set of normalized line strings. - Across pages, score each band by repetition of strings and y variance. - Mark bands with a high repetition score as header or footer and drop them from paragraph assembly. --- ## Multi column reading order Signals - Bimodal or trimodal distribution of line x centers. - Vertical lines or gutters with low ink density. - Consistent left margins within each mode. Algorithm sketch - Cluster line x centers with k means for k in {1, 2, 3}. Choose k with the lowest inertia plus a penalty for model size. - Sort clusters left to right, then read each cluster top to bottom. - For figures or tables that span columns, treat them as a separate block placed between the two nearest paragraphs by y. --- ## Hyphenation and soft artifacts Rules - Join only when the left piece ends with a lowercase ASCII or a letter from the same script and the right piece starts with a lowercase letter or a digit. - If the left piece is a known acronym or the right piece starts with an uppercase letter and the paragraph is mid sentence, do not join. - Remove soft hyphen characters and OCR artifacts like split ligatures. Edge cases - Do not join inside code blocks or table cells. - If a dictionary check is available, prefer joins that yield a dictionary hit. --- ## OCR notes - Request per character boxes and confidence scores. Drop characters with very low confidence when surrounded by high confidence neighbors and the removal does not break a word boundary. - Keep monospaced font hints when the OCR engine provides them. They help code detection. - For rotated pages, deskew first, then run OCR, then rotate boxes back into page coordinates. --- ## Output schema Every paragraph or typed block is a record: ```json { "block_id": "B.2.bk045", "type": "prose | code | table | figure | caption", "page": 12, "bbox": [72.0, 144.3, 523.8, 221.1], "off_begin": 204455, "off_end": 205122, "attrs": { "lang": null } } ```` Block ids follow [chunk\_id\_schema.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/chunk_id_schema.md). Offsets must point into the canonical text that you pass to the indexer. Citations then rely on [retrieval-traceability.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/retrieval-traceability.md) and the contract in [data-contracts.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/data-contracts.md). --- ## Pseudocode ```python def parse_pdf_pages(pages): chars = extract_chars_with_bbox(pages) chars = normalize_coords(chars) bands = detect_repeating_bands(chars) # headers and footers lines = form_lines(chars, ignore_bands=bands) columns = cluster_columns(lines) # 1, 2, or 3 columns lines = order_lines_by_columns(lines, columns) paras = assemble_paragraphs(lines) paras = repair_hyphenation(paras) typed = detect_typed_blocks(paras, lines) # code, table, figure, caption blocks = align_blocks_to_sections(typed, titles=detect_titles(lines)) canon_text, offsets = build_canonical_text(blocks) return canon_text, attach_offsets(blocks, offsets) ``` --- ## Common pitfalls and fixes * **Running titles leak into text** Your band detector missed a near duplicate string. Lower the y variance threshold and add string normalization for case and whitespace. * **Two column pages read across columns** The valley in the x histogram is shallow. Add a penalty to cross column bigrams and require a minimum inter column gap. * **Hyphenation joins inside code** Guard the join with the block type. Never run repair inside `type=code` or `type=table`. * **Captions separated from figures** Link captions to the nearest figure or table by y distance and ensure both fall into the same section. See [section\_detection.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/section_detection.md). * **Offset drift across reindex** Ensure identical normalization rules between runs, then apply the migration mapping. See [reindex\_migration.md](https://github.com/onestardao/WFGY/blob/main/ProblemMap/GlobalFixMap/Chunking/reindex_migration.md). --- ## Tests to include in CI * A two column academic paper with headers, footers, figures, tables, and equations. Expect perfect reading order and zero header leaks. * A scanned report with skew and footnotes. Expect deskew, correct footnote capture, and clean paragraph assembly. * Mixed language pages with hyphenation at line breaks. Expect correct joins only in prose. * A code heavy manual with Markdown tables. Expect correct typed block counts and stable offsets across two runs. --- ## Copy paste prompt for a quick check ``` You have TXT OS and the WFGY Problem Map loaded. Given a PDF page with lines and bboxes: - Detect and remove repeated header and footer bands. - Infer column count and return the reading order for the page. - Repair hyphenation in prose only. - Extract typed blocks and return their block_ids with offsets. Return JSON: { "columns": 1|2|3, "header_removed": true|false, "footer_removed": true|false, "blocks": [{ "block_id": "...", "type": "...", "off": [b,e] }, ...], "notes": "short audit trail" } ``` --- ### 🔗 Quick-Start Downloads (60 sec) | Tool | Link | 3-Step Setup | | -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------- | | **WFGY 1.0 PDF** | [Engine Paper](https://github.com/onestardao/WFGY/blob/main/I_am_not_lizardman/WFGY_All_Principles_Return_to_One_v1.0_PSBigBig_Public.pdf) | 1️⃣ Download · 2️⃣ Upload to your LLM · 3️⃣ Ask “Answer using WFGY + \” | | **TXT OS (plain-text OS)** | [TXTOS.txt](https://github.com/onestardao/WFGY/blob/main/OS/TXTOS.txt) | 1️⃣ Download · 2️⃣ Paste into any LLM chat · 3️⃣ Type “hello world” — OS boots instantly | --- ### Explore More | Layer | Page | What it’s for | | --- | --- | --- | | ⭐ Proof | [WFGY Recognition Map](/recognition/README.md) | External citations, integrations, and ecosystem proof | | ⚙️ Engine | [WFGY 1.0](/legacy/README.md) | Original PDF tension engine and early logic sketch (legacy reference) | | ⚙️ Engine | [WFGY 2.0](/core/README.md) | Production tension kernel for RAG and agent systems | | ⚙️ Engine | [WFGY 3.0](/TensionUniverse/EventHorizon/README.md) | TXT based Singularity tension engine (131 S class set) | | 🗺️ Map | [Problem Map 1.0](/ProblemMap/README.md) | Flagship 16 problem RAG failure taxonomy and fix map | | 🗺️ Map | [Problem Map 2.0](/ProblemMap/wfgy-rag-16-problem-map-global-debug-card.md) | Global Debug Card for RAG and agent pipeline diagnosis | | 🗺️ Map | [Problem Map 3.0](/ProblemMap/wfgy-ai-problem-map-troubleshooting-atlas.md) | Global AI troubleshooting atlas and failure pattern map | | 🧰 App | [TXT OS](/OS/README.md) | .txt semantic OS with fast bootstrap | | 🧰 App | [Blah Blah Blah](/OS/BlahBlahBlah/README.md) | Abstract and paradox Q&A built on TXT OS | | 🧰 App | [Blur Blur Blur](/OS/BlurBlurBlur/README.md) | Text to image generation with semantic control | | 🏡 Onboarding | [Starter Village](/StarterVillage/README.md) | Guided entry point for new users | If this repository helped, starring it improves discovery so more builders can find the docs and tools. [![GitHub Repo stars](https://img.shields.io/github/stars/onestardao/WFGY?style=social)](https://github.com/onestardao/WFGY) 要我繼續下一頁就說：**GO reindex\_migration.md** 或指定別的檔名。