Posterization
Smooth gradients crushed into a few flat bands of color, like a screen-printed concert poster.
See it
What it is
Posterization quantizes tone: instead of 256 levels you allow 3 or 4, so every smooth gradient collapses into flat plateaus with hard steps between them. Where you apply it matters. Quantize luminance and you get exactly 3 or 4 tonal bands. Quantize each channel separately, which is what most Posterize sliders actually do, and 4 reds times 4 greens times 4 blues can yield up to 64 distinct colors, which is why a posterized photo often shows more bands than the number you typed. The name comes from screen-printed posters, where each color was a separate ink and a separate pass.
Use it when a photo needs to become a graphic mark: the Shepard Fairey 'Hope' poster is four tones, and most Warhol-style prints and cel-shaded looks are the same move. Posterizing after a gradient map is the trick for controlling exactly which color each band lands on.
Gotcha: this is the same math as banding, the bug. The difference is intent and step count, so commit hard (3 to 5 levels) rather than hovering at 12, where it just looks like a broken gradient. Skin and soft-focus areas fall apart first, so blur slightly before quantizing to keep the bands as clean shapes instead of ragged confetti.
Ask AI for it
Posterize this image: quantize its luminance into exactly 4 flat levels with hard edges between bands, no dithering and no gradient left anywhere. Map the 4 levels to a fixed screen-print palette (deep navy, brick red, warm cream, off-white) so it reads as a 4-color propaganda poster. Blur the source slightly first so the band boundaries come out as clean shapes.