EXH-03sample entry — swap with a real artifact

Riso Poster Lab

A generative poster tool that mimics two-ink risograph printing — misregistration, halftones and all — in a 12KB page.

generative
canvas
design-tool

Overlapping amber and blue halftone discs on warm paper, like risograph inks

Model: Claude (Fable 5)
Iterations: 3
Time to ship: 7h
Shipped: Mar 21, 2026

The prompt · verbatim

Build a browser tool that generates risograph-style posters. Canvas 2D only. The riso look is non-negotiable and has exactly three parts:

1. TWO INKS ONLY. Every poster is two spot colors multiplied over paper — never full RGB. Offer 5 curated ink pairs, not a color picker.
2. MISREGISTRATION. The second ink layer is offset by 2-6px at a random angle, like a real drum shift. This must be subtle enough to feel accidental.
3. HALFTONE. Continuous tones become dot grids. Dot size maps to luminance; the grid angle differs per ink (15° / 75°).

COMPOSITION: generate abstract geometric compositions (blobs, bars, arcs) with a strong focal point — use a simple rule like "one big element, two medium, scattered small". Seeded randomness: the same seed must always reproduce the same poster, and the seed is shown in the corner so people can share it.

EXPORT: PNG at 2x. The whole page under 15KB of JS, no dependencies.

Do not add UI chrome beyond: regenerate, ink pair selector, seed field, download. The poster is the interface.

Why it works

The aesthetic is decomposed into mechanics. “Riso style” alone produces clip-art; misregistration offsets in pixels, halftone angles in degrees, and a two-ink multiply rule produce the real thing.
Curated ink pairs instead of a color picker is a product decision embedded in the prompt — constraints presented as features.
Seeded randomness with a visible seed makes the tool shareable and the output reproducible, which turns a toy into a tool.