Maxim Dolgolyov
8a7091ddec
Копия пользовательской автопамяти (29 фактов + индекс MEMORY.md) в .claude/memory/, чтобы переносить между машинами через git. README.md — как восстановить в пользовательскую папку на другой машине. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
81 lines
2.9 KiB
Markdown
81 lines
2.9 KiB
Markdown
# Image Extraction from PDF — ЦТ/ЦЭ Questions
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## Tools available
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- **pdftoppm** (poppler, via scoop): renders PDF pages to PNG
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- **sharp** (npm, installed in `backend/`): crops images in Node.js
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- Script: `backend/src/db/crop_images.js`
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## Workflow for extracting figures from exam PDF
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### Step 1 — Render pages at 200 DPI
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```bash
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pdftoppm -png -r 200 -f <first_page> -l <last_page> "path/to/file.pdf" "/tmp/prefix"
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# Output: /tmp/prefix-06.png, /tmp/prefix-07.png ...
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# Copy to: frontend/img/questions/pageN.png
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```
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### Step 2 — Calibrate coordinates using 72 DPI reference
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```bash
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pdftoppm -png -r 72 -f <first_page> -l <last_page> "path/to/file.pdf" "/tmp/pt"
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# Output: /tmp/pt-06.png etc. (614×844 px for A4)
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# Copy to: frontend/img/questions/ptN.png
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```
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At 72 DPI: A4 = 614×844 px. Scale to 200 DPI: **×2.777**
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Measure coordinates visually on 72 DPI images, multiply by 2.777 to get 200 DPI coords.
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### Step 3 — Test crops (Node.js)
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```javascript
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// Run from backend/ folder
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const sharp = require('sharp');
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sharp('../frontend/img/questions/pt6.png')
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.extract({ left: 220, top: 80, width: 200, height: 100 })
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.toFile('../frontend/img/questions/test.png');
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```
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### Step 4 — Run crop_images.js
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```bash
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cd backend && node src/db/crop_images.js
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```
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---
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## ЦТ 2021 — Variant 1 crop coordinates (200 DPI, 1705×2344)
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| File | Question | Source page | left | top | width | height |
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|------|----------|-------------|------|-----|-------|--------|
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| ct2021v1_a1.png | A1 triangle | page6.png | 611 | 222 | 556 | 292 |
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| ct2021v1_a7.png | A7 graph f(x) | page6.png | 278 | 1222| 750 | 403 |
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| ct2021v1_a15.png | A15 parabola | page7.png | 556 | 917 | 695 | 278 |
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| ct2021v1_a17.png | A17 grid A,B | page7.png | 861 | 1439| 639 | 194 |
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| ct2021v1_a18.png | A18 pyramid | page7.png | 389 | 1656| 945 | 472 |
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| ct2021v1_b1.png | B1 bar chart | page8.png | 28 | 83 | 1167| 556 |
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| ct2021v1_b3.png | B3 3D planes | page8.png | 1015| 1717| 319 | 417 |
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| ct2021v1_b4.png | B4 enclosure | page9.png | 945 | 14 | 542 | 208 |
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PDF source: `ЦТ-ЦЭ/ЦТ 2021.pdf`
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- Page 6 = Variant 1, Part A (A1–A11)
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- Page 7 = Variant 1, Part A (A12–A18)
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- Page 8 = Variant 1, Part B (B1–B3)
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- Page 9 = Variant 1, Part B (B4–B14)
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Images stored: `frontend/img/questions/ct2021v1_*.png`
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Served at: `/img/questions/ct2021v1_*.png` (via express.static on frontendDir)
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---
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## DB: updating image field after seeding
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```javascript
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const upd = db.prepare('UPDATE questions SET image = ? WHERE text LIKE ? AND year = ?');
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upd.run('/img/questions/ct2021v1_a1.png', '[ЦТ 2021 · A1]%', 2021);
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```
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---
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## Notes
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- PDF contains scanned raster images — no extractable vector graphics
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- Each PDF page = one large bitmap scan
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- `pdfimages` extracts only full-page bitmaps (not individual diagram crops)
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- sharp must be required from `backend/` directory (installed there)
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- Temp page renders NOT committed to git — regenerate with pdftoppm when needed
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