Prompts for Posters

A poster is looked at from four metres away by someone who is walking past. That single fact decides nearly everything about how you should prompt for one. Big shapes, few colours, one clear subject, hard edges. Anything that needs you to lean in has already failed.

Most generated posters look wrong because the prompt asked for a picture rather than for a poster. A picture can be soft, detailed and evenly lit. A poster has to hit a wall of visual noise and win, which means the prompt has to be about graphic force before it is about subject matter.

Ask for Flat, Not Photographic

The reliable way in is to name a print medium. Screen print, risograph, letterpress, offset lithograph, woodblock — each of these carries a whole set of properties you would otherwise have to spell out: limited colour, flat fills, visible registration, slightly rough edges. “Two-colour screen print, black and orange” gets you closer to a real poster in six words than a paragraph of adjectives ever will.

Naming a design tradition works just as well. Swiss International style, Polish film poster, Bauhaus exhibition poster, mid-century travel poster, punk photocopy flyer. These are not vague moods; they are bodies of work with consistent geometry, palette and typographic space, and models have seen enough of each to reproduce the look.

Build the Type Area Into the Prompt

Almost every poster carries words, and almost nobody plans for them. Decide up front where the text block sits, then prompt the composition around it: subject in the lower two thirds, clean flat colour across the top, no detail in the upper band. You are generating a background plate for a layout, and it is much easier to design one deliberately than to rescue a full-bleed image afterwards.

The same goes for the edges. Print gets trimmed, so keep anything that matters away from the border and say so — “wide margin, subject well inside the frame”. A composition that runs right to the edge will lose a few millimetres of itself at the cutter.

Contrast Does the Work at Distance

When you assess a draft, squint at it or blur it heavily. What you should still see is two or three distinct masses of tone. If it turns into a single grey field, the poster has no structure, and no amount of detail will fix that — the fix is a stronger separation between subject and ground.

That usually means rewriting the prompt to be more extreme, not more precise. A darker background, a lighter subject, one saturated accent colour and everything else desaturated. Say “high contrast, limited palette, large simple shapes” and mean it. Posters that work tend to look almost crude up close, which is exactly why they read from across the room.