Screen E022 · diffusion

Receipt

Thermal paper: one bit, error diffusion, and a print head that does not heat evenly.

How it works

Atkinson error diffusion to a single bit — the algorithm the first Macintosh shipped with, and the one a thermal printer still uses, because a heating element either burns the paper or it does not. On top of it, a per-row gain that rises and falls: a real print head warms up and cools down, and that is what leaves the horizontal banding on a till receipt.

What to touch

Heat is the one to touch: at zero the diffusion is clean, and as it climbs the bands appear and the blacks open up. Pixel sets how big each burnt dot is, and Contrast decides how much of the picture survives one bit.

What it suits

Faces, logos and anything with a clear silhouette. One bit has no midtones to hide in, so a flat picture comes out flat.

On the three lattices

Receipt can be laid on a cartesian, a polar or a hexagonal lattice. The grid is an axis of its own, so the same screen gives three different pieces.

Other screens

• Dots — One mark per cell, radius proportional to ink. The plainest screen there is, and the one that survives any image.
• Halftone — A rotated screen at a real printing angle. Dot area follows the square root of ink, the way a press actually lays tone.
• Burin — Short strokes that follow the contours of the image, steered by a tangent field taken from the picture itself with a Sobel operator.
• Dither — Error diffusion walked in serpentine so the grain has no direction. Five algorithms: Floyd–Steinberg, Atkinson, Bayer, blue noise and modulated line.
• ASCII — A character per cell, with the ramp ordered by the ink each glyph actually covers — measured by rendering it, not guessed from a table.
• Glyph — The same ramp with the cell filled and the letter turned by tone. Type as texture rather than type as text.

Open Receipt in the studio · Index of screens