PNG Posterize Tool — Reduce Colour Levels

What posterising does

Posterising reduces the number of unique colours in an image to a small palette. Instead of 16.7 million possible colour combinations (256 × 256 × 256 for full 8-bit RGB), a posterised image uses only a few hundred or even just a few dozen. The result is a flat, graphic, illustrated look — bold colour regions instead of smooth gradients, hard transitions instead of subtle blends. It's the same visual style as classic screen-printed posters, comic-book art and the Andy Warhol Marilyn Monroe series.

"Levels per channel" controls how aggressive the reduction is. At 2 levels per channel, each of red/green/blue is reduced to just 2 values (0 or 255) — total palette of 2³ = 8 colours. At 4 levels per channel, 4³ = 64 colours. At 8 levels per channel, 8³ = 512 colours, which already starts to look like a normal photo with some banding.

Levels per channel — what each setting gives you

• 2 levels — 8-colour palette. Extreme posterise. Looks like a printed political poster or warning sign.
• 3 levels — 27-colour palette. Strongly graphic but still recognisable as a photo.
• 4 levels — 64-colour palette. The default. Vintage cartoon / comic-book look.
• 5–6 levels — 125–216 colours. Subtle posterise, useful for stylising photos without making them look "filtered".
• 7–8 levels — 343–512 colours. Light banding only visible in smooth gradients (skies, skin).

When posterising works well

• Concert/movie posters — high impact, low colour count, retro vibe.
• Screen-printing prep — print runs need a small number of distinct colours.
• Illustration mock-ups — quickly turn a reference photo into a stylised graphic.
• T-shirt and merch design — fewer colours = cheaper print runs.
• Comic-book style images — flatten photos into cel-shaded looks.
• Wallpapers and tile patterns — flat colours create a clean, modern aesthetic.
• Reducing PNG file size — posterised PNGs compress dramatically smaller (fewer unique colours = better PNG compression).

How this tool works

Each pixel's R, G, B values are independently quantised to the chosen number of levels. With L levels, the channel value v (0–255) is mapped to round(v / 255 × (L-1)) × 255 / (L-1). So at L=4, valid output values are 0, 85, 170, 255. The mapping is applied to every pixel; the alpha channel is left unchanged so transparency is preserved.

The operation is fast (one pass through the pixel array) and runs entirely in your browser. There's no upload, no queue, no waiting on a server.

Posterise vs. threshold vs. dither — what's the difference?

Threshold reduces to exactly 2 colours: pure black and pure white. Posterise reduces to a small palette of several colours but keeps the colour information. Dither (not available in this tool) achieves a similar palette reduction but breaks up the colour blocks with patterns of pixels to fake smoother transitions — useful for game art and pixel-perfect retro looks. For natural-looking flat-colour posters, plain posterise is usually what you want.

Tips and best practice

• Combine posterise with the Brightness/Contrast tool — raise contrast slightly before posterising to make the colour bands more distinct.
• For maximum graphic impact, run a strong saturation boost (140–160%) after posterising. Flat colours look more vivid.
• If posterise produces visible "banding" in smooth gradients (sky, skin), raise the level count or apply a small amount of blur first.
• For screen-print preparation, work with exactly the level count that matches your number of print colours. 2 = 2-colour print, 3 = 3-colour, etc.
• Posterise tends to look weak on already-flat images (logos, screenshots) — it shines on photos with rich tonal variation.

FAQs

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