Dither & Duotone

What it's for

Reduce a picture to a few colours the way old computers, games consoles, newspapers and e-ink screens do, with dithering that mixes dots of the colours you have to suggest the ones you don’t, or make a two-colour duotone.

For example, when you want a 1-bit black and white image for a retro look, a thermal printer or an e-ink display, choose Atkinson dither and Black and white for the classic early Mac look.

How to use it

Choose a picture (or drop or paste one). Then choose the Effect:

• Floyd–Steinberg, Atkinson and Stucki spread each pixel’s rounding error to its neighbours, for natural grain; Atkinson spreads less and keeps more contrast.
• Ordered (Bayer) uses a regular cross-hatch pattern, as on early screens and printers.
• Nearest colour just rounds each pixel to the closest colour, giving flat bands.
• Duotone maps the dark-to-light range onto two colours you choose for the Shadows and Highlights.

For the dithers, choose the Colours: black and white, four greys, the Game Boy, CGA or PICO-8 palettes, eight primaries, The picture’s own main colours (as many as you say), or My own hex codes. Pixel size makes each dot a block of that many pixels, and Width at most shrinks the picture first. Save as PNG saves the result. All the settings are remembered.

Example

Choose any photo, then set:

Effect: Ordered (Bayer) dither · Colours: Game Boy · Pixel size: 3 · Width at most: 480

The photo comes out in the four Game Boy greens, in a regular pattern of chunky pixels, 480 pixels wide.

Good to know

Colours are matched by weighted RGB distance, which is quick but not perceptually exact. Large photos take a moment with error diffusion; set Width at most to speed it up. Transparency is kept as it is, not dithered. The picture doesn’t leave your browser.