2 commits

Author	SHA1	Message	Date
jedarden	ff82fdce90	feat(pdftract-5xyjv): implement 3x3 median-filter denoising for OCR preprocessing ... - Add median_denoise() function using imageproc::filter::median_filter - 3x3 kernel (radius 1,1) removes salt-and-pepper noise while preserving edges - Comprehensive tests: noise removal, edge preservation, binary output - Export median_denoise from ocr::preprocessing module Closes: pdftract-5xyjv	2026-05-24 16:09:08 -04:00
jedarden	61b94b49d2	feat(pdftract-6dki1): implement histogram stretch contrast normalization ... Implement Phase 5.3.2a: histogram-based contrast normalization for OCR preprocessing. The algorithm stretches the input gray value range (from 1st to 99th percentile) to the full [0, 255] output range, improving downstream binarization effectiveness. Key implementation details: - 256-bin histogram computation for percentile calculation - 1st/99th percentile robustness against hot pixels and artifacts - In-place mutation for performance (no double allocation) - Proper error handling for uniform images and invalid dimensions - Overflow-safe arithmetic using i32 intermediate values Acceptance criteria: - Image with [50, 200] range → stretched to [0, 255] - Hot pixel robustness: single 0/255 pixels handled correctly - Uniform image → early return with UniformImage error - Invalid dimensions (zero width/height) → InvalidDimensions error - Full performance: < 50 ms for 8 MP images Closes: pdftract-6dki1	2026-05-24 10:30:20 -04:00