Step 1: scan_quality.py — Laplacian blur + contrast scoring, adjusts
OCR confidence threshold (40 for good scans, 30 for degraded).
Quality report included in API response + shown in frontend.
Step 2: max_columns parameter in cv_words_first.py — limits column
detection to 3 for vocab tables, preventing phantom columns D/E
from degraded OCR fragments.
Step 3: ocr_image_enhance.py — CLAHE contrast + bilateral filter
denoising + unsharp mask, only for degraded scans (gated by
quality score). Pattern from handwriting_htr_api.py.
Frontend: quality info shown in extraction status after processing.
Reprocess button now derives pages from vocabulary data.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
