Image Posterize
Reduce each channel to N levels for a poster-style look.
Overview
The Image Posterize tool reduces the number of distinct intensity levels in each colour channel of an uploaded image, producing the flat, banded look of a silk-screen print or a pop-art poster. Pick a level count between 2 and 16 per channel and the tool returns a re-encoded copy with smooth gradients collapsed into hard, blocky steps.
It is the right effect for poster artwork, T-shirt graphics, retro game tributes, and any place a graphic designer wants to give a photo a more illustrative, less photographic feel. Marketing teams use it on hero photography to match a brand's vintage or risograph aesthetic without redrawing the image.
How it works
A standard 8-bit channel holds 256 possible values. Posterising to N levels divides that range into N equal-width buckets and snaps every input value to the centre of its bucket. The formula is roughly output = round(input * (N - 1) / 255) * (255 / (N - 1)), which is applied independently to red, green and blue.
Because each channel is quantised independently, the total number of possible output colours is N^3 — a 4-level posterise produces up to 64 distinct colours, a 2-level posterise just 8. The hard transitions between buckets are exactly what creates the banded "poster" feel; unlike dithering, no error is diffused to soften the boundary.
Examples
Photo posterised to 2 levels per channel → 8 colours total,
classic high-contrast pop-art poster.
Photo posterised to 4 levels per channel → 64 colours,
smooth-looking gouache illustration vibe.
Photo posterised to 8 levels per channel → 512 colours,
subtle banding that mimics offset printing.
Photo posterised to 16 levels → barely distinguishable from the
original on a normal monitor.
FAQ
What's the difference between posterise and quantise?
Posterise treats every channel independently with the same bucket count. Quantise picks a global palette of N colours optimised for the image. Posterise is faster but coarser; quantise gives a tidier final palette.
How is it different from dithering?
Dithering diffuses quantisation error across neighbours to fake intermediate colours. Posterise leaves the error in place, which is what produces the signature banding.
Will the output have an alpha channel?
Yes — alpha is preserved unchanged. Only the RGB channels are quantised.
What's the lowest useful level count?
Two per channel produces only 8 final colours and is the most graphic-looking result. Anything below that is more easily produced with a threshold or quantise tool.
Can I posterise just the luminance channel?
The bundled implementation quantises RGB. A luminance-only posterise would keep colour smooth while banding brightness — that requires a separate Lab-space variant.