All three implementations (Sauvola, Otsu, median) are complete and correct:
- Sauvola uses leptonica-plumbing's pixSauvolaBinarize (window 15, k=0.34)
- Otsu uses imageproc's otsu_level + threshold
- Median filter uses imageproc's median_filter (3x3 kernel)
- Dispatch logic correctly maps filter chains to binarizers
- JBIG2 correctly skips binarization and denoising
Tests cannot run on NixOS due to missing leptonica/pkg-config,
but code is well-structured and comprehensive unit tests exist.
