Image dithering for laser engraving

In normal image mode a laser fires at full power or not at all. A photo is made of greys, so something has to decide which spots get burned. The simplest answer is a threshold: everything darker than 50% burns, everything lighter does not. On a portrait that throws away almost all the tone, which is why threshold files look like photocopies.

Dithering keeps the tone by changing how many dots burn in an area. More dots read darker, fewer read lighter. From normal viewing distance the eye blends the dots back into greys. The examples on this page show the same photo engraved on wood with a 50% threshold, with Floyd and Steinberg, and with our Ultra dither.

Error diffusion walks the image pixel by pixel. Each pixel becomes burn or no-burn, and the difference between what it wanted and what it got (the error) is pushed onto the neighbours that have not been decided yet. The kernels differ in how far and in what proportions they spread that error.

• Floyd and Steinberg spreads the error to four neighbours. Fast and sharp, the classic, but it can draw wormy lines in smooth areas.
• Jarvis, Judice and Ninke spreads it over twelve neighbours across two rows. Smoother and less wormy.
• Stucki uses the same reach as Jarvis with different weights. Very smooth gradients. It is the default on cork.
• Burkes is a lighter two-row kernel. Crisp with a slight texture.
• Sierra, Sierra Two-Row and Sierra Lite go from balanced (close to Jarvis) to the fastest diffusion.
• Atkinson only passes on 6/8 of the error. High contrast and clean highlights, but shadow detail drops out.

Bayer 4×4 and Bayer 8×8 are ordered dithers. Instead of spreading error they compare each pixel with a fixed repeating matrix, which gives a regular cross-hatch pattern. It looks retro and stays very even, which some people like on tiles and metal. Threshold 50% is pure black and white, best for logos and text, not for photos.

No dithering keeps the greys. Use it only if your laser and software engrave in grayscale mode with variable power, or for 3D engraving. If your software is set to threshold, a grayscale file will lose its tones.

Ultra is a Direct Binary Search dither. Instead of deciding each dot once and moving on, it keeps moving and swapping dots and checks whether the result looks closer to the photo, as seen through a model of the eye and the laser spot. It stops when no move makes it better. That takes a few seconds per image rather than a fraction of a second, which is why the app shows a quick preview first.

Ultra is the default for every material preset except cork, where Stucki is the default because cork's grain hides fine detail anyway. You can switch dither on any image in Easy Mode. How Ultra measures up against other tools is on the comparison page, with the method.

Start with the preset's default. If a portrait looks too soft from a distance, try a Look such as Punchy before you change the dither. Change the dither when you want a specific texture: Atkinson for bold, poster-like pet portraits, Bayer for an even graphic pattern, Threshold for line art. Serpentine scanning, where the direction alternates on every row, is used to reduce directional worm artifacts in error diffusion.

Your laser's DPI matters as much as the dither. Dots that overlap merge into blotches. Check your setting with the DPI calculator.