Image Dither

Image Dither converts a full-colour photograph into an image built from a small fixed set of colours, using a pattern of dots or blocks to simulate the tones that were removed. It is the effect behind newspaper photographs, the original Macintosh screen, Game Boy sprites and screen-printed gig posters, and this tool reproduces all of them from a single upload.

Dithering exists because a display or a printing press often cannot reproduce every tone in a photograph. A newspaper press has one colour of ink and one colour of paper; a 1984 Macintosh had one bit per pixel. Rather than round every pixel to the nearest available colour and lose the gradient entirely, a dither algorithm distributes the rounding error across neighbouring pixels, so that at normal viewing distance the eye averages a cluster of black dots on white paper back into grey. Different algorithms distribute that error differently, and the distribution is what gives each one its signature look.

Six algorithms are available. Bayer 4x4 uses an ordered threshold matrix, producing the regular crosshatch familiar from early PC games. Atkinson, written by Bill Atkinson for the original Macintosh, pushes only three quarters of the error to its neighbours, which blows out highlights and yields the high-contrast look of MacPaint. Floyd-Steinberg distributes the full error across four neighbours for the most photographically faithful result. Halftone samples along a rotated lattice and varies dot radius with tone, the way a real halftone screen is angled on press. Cyber Glitch snaps colours to the palette and displaces scanlines. Hard 1-Bit is a straight threshold cut with no dithering at all.

Everything runs client-side. The image is decoded, cropped and dithered by your own browser using the Canvas API, and no copy is ever sent anywhere, which matters when the source is an unreleased photograph or a client asset. Output is available as PNG at up to 8x the stage resolution, or as SVG, where each dot is written as a real vector shape so the poster can be scaled to any print size or opened in a vector editor for further work.