Rendering Gray from Pure Black and White

Threshold, random, and blue-noise dithering

One grayscale image rendered in pure black and white three ways: hard threshold, random threshold, blue noise One grayscale image rendered in pure black and white three ways: hard threshold, random threshold, blue noise

The same synthetic grayscale image (a radial-gradient sky with a sun, a dark church spire carrying faint brickwork, and a black-to-white gray ramp along the bottom) converted to pure black and white three ways. A single threshold at 50% brightness collapses dark regions to featureless black and light regions to featureless white; an independent random threshold per pixel brings the grays back but clumps into hot and cold spots at every scale; blue-noise dithering via a genuine void-and-cluster mask (Ulichney 1993), randomness with the single relational constraint of maintaining distance from your neighbors, renders every shade faithfully while every pixel stays pure black or white.