binarization

Forcing every pixel in an image down to pure black or pure white, usually to separate ink from paper.

Binarization forces every pixel down to pure black (ink) or pure white (paper) -- a point operation built from thresholding. A single global threshold, hand-picked or chosen automatically by Otsu's method, works well on an evenly lit scan; a photo with uneven lighting needs adaptive (local) thresholding instead.

Examples

Otsu's method picks one global brightness cutoff for an evenly lit scan, turning every pixel below it black and every pixel above it white.