Posterize a PNG
Posterizing collapses smooth shading into a small number of flat tones, the way a screen print or a limited-run poster does. Set the number of levels each colour channel is allowed and watch gradients snap into hard-edged bands.
Drop images here
Multiple files allowed
Levels are per channel, not total
This is the number that confuses people. "4 levels" means each of red, green and blue is rounded to one of 4 values — so the total palette is up to 4³ = 64 colours, not 4. Two levels per channel gives 8 colours (the corners of the RGB cube: black, white, and the pure primaries and secondaries), which is the hard poster look. Three gives 27, four gives 64, eight gives 512 and starts looking almost normal.
Below about 6 levels the effect is unmistakable and graphic. Above about 12 it's mostly invisible on photographs, though it can still be useful as a subtle flattening pass before other effects.
Posterize versus reduce colours
Both cut the number of colours, and they do it in opposite ways. Posterize rounds each channel to a fixed grid — the palette is decided in advance by arithmetic, regardless of what's in your image. That's why it looks stylised: the colours are not your image's colours, they're the grid's.
Reduce colors derives a palette from the image with median cut, so it picks the colours that are actually present and picks them adaptively. That's what you want when the goal is a smaller file that still looks like the original. Come here for the aesthetic; go there for the compression.
Posterize pairs well with PNG to SVG — flat bands trace into far fewer vector shapes than a continuous-tone photo — and with Edge detect overlaid via Overlay images for a comic-book effect.
FAQ
Why do I see banding in the sky?
That's the effect working. Smooth gradients are exactly what posterizing turns into visible bands. If you want fewer colours without bands, use Reduce colors with dithering on.
Does it make the file smaller?
Usually yes, sometimes substantially, because large flat areas compress well. But that's a side effect — Reduce colors is the tool built for it.
Is transparency affected?
No. Only the colour channels are quantised; alpha passes through at full precision, so soft edges stay soft.
Can I posterize to specific colours?
Not here — the levels are an even grid. For a chosen palette, remap individual colours with Change color or apply a gradient map.