Dithering methods for laser engraving

Most photo engraving works with dots that are either burned or left alone. A grey tone is therefore made from a mix of burned and unburned dots: dense dots read as dark, sparse dots as light. Dithering is the rule that decides where those dots go. The same photo at the same size can look soft, crisp, grainy or patterned depending on the method, which is why the choice matters as much as speed and power.

• Grey is made from dot density
• The method decides the texture
• Same photo, very different results

Error-diffusion methods round each pixel to burned or not burned and pass the rounding error on to the pixels that have not been processed yet. Floyd-Steinberg spreads it over four neighbours: fast, fine-grained, sometimes with worm-like streaks in flat areas. Jarvis and Stucki spread it over twelve neighbours across two rows, which gives smoother gradients; Stucki usually looks a little sharper than Jarvis. Atkinson passes on only part of the error, so the lightest and darkest tones clip — the result is lighter and more contrasty, which suits high-contrast motifs.

• Floyd-Steinberg: fine, fast, can streak in flat areas
• Jarvis and Stucki: smoother gradients, Stucki a bit sharper
• Atkinson: lighter, more contrast, clipped extremes

Ordered dithering places dots by a fixed threshold grid, which creates a regular, cross-hatch-like texture that is very predictable from piece to piece. Halftone and newsprint group dots into round cells that grow with darkness, like printed newspaper photos — a deliberate graphic look. Blue noise spreads dots evenly without a visible pattern and without the streaks error diffusion can leave. Which is best depends on the material: light woods show fine error diffusion well, while coarse or dark materials often hold a patterned method better.

• Ordered: regular texture, very repeatable
• Halftone and newsprint: printed, graphic look
• Blue noise: even dots, no visible pattern

Grayscale is the alternative to dithering: instead of dot density, the laser varies its power per pixel. It needs a laser that responds evenly to small power changes. In Vextrify, diode lasers with GRBL controllers can receive grayscale, while CO2 lasers with Ruida controllers are sent a dithered dot pattern. Text and logos are a different case: dithering breaks their edges into ragged dots. Use a threshold, or better vectors, for anything with lettering.

• Grayscale: power varies per pixel
• Vextrify: grayscale for GRBL diodes, dithering for Ruida CO2
• Text and logos: threshold or vectors, never dither