The short answer
Use greyscale when the material darkens gradually with power — many woods and coated materials do — and when your controller modulates power cleanly at the speed you engrave. Use dithering when the material is essentially binary, when your controller cannot modulate power reliably, or when you want a predictable, repeatable structure. On materials like anodised aluminium or slate, where the mark is either there or not, dithering usually looks better than a greyscale ramp that the material cannot express.
Material reacts gradually to power → greyscale is worth trying
Material marks or does not mark → dithering
Unsure about your controller → dithering is the safe default
Which dither pattern for which job
Error-diffusion patterns spread the rounding error to neighbouring pixels, which produces the irregular, photographic look: Floyd-Steinberg is the classic, Jarvis and Stucki spread further and look smoother at the cost of some sharpness, Atkinson leaves highlights cleaner and is popular for portraits on wood. Ordered and clustered patterns place dots on a fixed grid, which gives a deliberately graphic, screen-printed appearance and is more forgiving when the burn spreads. A pure threshold is not a photo tool — it is for line art and logos.
Floyd-Steinberg: the dependable photographic default
Jarvis and Stucki: smoother, slightly softer
Atkinson: cleaner highlights, good for portraits
Ordered and halftone: deliberate graphic look
Threshold: line art, not photos
What this means in practice
Dot density and burn spread interact: a fine pattern on a material that spreads heavily will merge into a solid tone, which is the usual cause of a dark, flat result. If your engraving looks too dark overall, a coarser pattern often fixes more than reducing power. And whichever mode you choose, the light end matters most — areas that should be untouched material must not pick up stray dots, or the whole picture gains a grey veil.
Fine pattern plus heavy spread equals solid tone
Too dark? Try a coarser pattern before cutting power
Untouched areas must stay untouched
How Vextrify helps
Photo Studio offers both routes side by side: a greyscale mode that maps tone to power per pixel, and ten dot patterns including Floyd-Steinberg, Jarvis, Stucki, Atkinson, ordered, halftone, newsprint and blue noise. You see the result at engraving size before you commit a workpiece, and the choice is stored with the material recipe, so the next job starts where the last one ended. The browser version is free and needs no account.
Greyscale and ten dot patterns in one place
Preview at engraving size, not at screen size
Stored with the material recipe