Posterize a photo
N levels per channel turns a photo into flat bands — the graphic look of screen-print and propaganda posters.
Tools used in this guide
The job
Quantizing each RGB channel to 2–16 levels destroys gradient detail and leaves bold bands — great for stencil art, retro graphics, and testing how a palette survives reduction.
Levels
Pick an image and a level count. 4 levels per channel gives 4³ = 64 possible colors; 2 gives the starkest 8-color graphic look.
Worked example
A sunset at 4 levels: the smooth sky gradient becomes three distinct orange bands — instantly silk-screen. At 16 levels the eye barely notices the quantization.
Where it stops
Uniform quantization — it doesn't pick the smartest palette (that's a different algorithm, see color-palette). Alpha is preserved; output matches the input format.