Ditherer

What dithering is

A screen shows millions of colours; a Game Boy showed four and a laser printer shows one. Dithering is the trick that makes a picture survive the drop. Where a pixel cannot be grey, the algorithm decides whether it should be black or white and remembers how wrong that was, so the next pixels lean the other way. Step back and the dots average out into the tone that was there. Your eye does the last part of the work.

The error-diffusion family (Floyd-Steinberg, Atkinson, Burkes, Sierra, Stucki, Jarvis-Judice-Ninke) pushes that rounding error onto the pixels to the right and below, each with its own set of weights. Serpentine scanning runs alternate rows backwards so the error does not drift into diagonal worms. Atkinson throws a quarter of the error away on purpose, which is why the old Macintosh look is lighter and crisper than Floyd-Steinberg. Ordered dithering (Bayer) skips the memory: it compares each pixel against a fixed crosshatch pattern, so the same picture always gives the same dots, and it is what games and demos used because it costs nothing. Halftone is the printing trade's version: a grid of round dots turned to an angle, each dot sized to how dark its cell is, which is the texture of every newspaper photo ever printed. Threshold is what you get with no dithering at all.

Getting a good one

Pixel size is the whole game. At 1 the dots are one screen pixel and a photo comes out looking like a photo. At 3 or 4 the pattern becomes the picture, which is usually what people mean when they ask for the dithered look. Game Boy at pixel size 3 with Bayer 4x4 is the one to try first. If a picture goes muddy, push contrast up until the shapes separate, then bring gamma down a touch for darker mids or up for lighter ones.

The tone palettes (Macintosh, Game Boy, newspaper, amber, your own two) turn the picture grey first and spread it across the palette's levels evenly. CGA quantises in colour: every pixel goes to the nearest of the four and the error is carried per channel, so a blue sky comes out as a cyan and magenta weave, which is exactly what 1983 looked like.

Download PNG saves the dithered picture at its working size, or doubled or quadrupled with hard pixels, no smoothing. Copy image puts the same PNG on your clipboard where the browser allows it. Nothing you drop, paste or pick is sent, logged or stored. The only thing this page records is that a render happened, with which algorithm and palette.