An engraved photograph lives or dies in the setup, and the photo-engraving guide carries the four facts that set it up right: the resolution rule, the grey conversion, the dither kernels, and presets that say out loud what they are.
Resolution: the interval is the DPI
The photo's detail is decided by the line interval — the spacing between scan lines. Pixels across the picture = size ÷ interval, and in the other direction DPI = 25.4 ÷ interval. The app defaults to 0.1 mm = 254 DPI, sitting inside LightBurn's suggested 120–300 DPI window (0.08–0.2 mm). The window has walls for real reasons: below 120 DPI faces soften; above 300, the beam's own spot cannot resolve the extra lines, so the dots stop being dots.
Tone: the grey the machine will burn
Colour photographs become a single grey channel before the beam sees them, converted by the broadcast-standard luma weights (ITU-R BT.601):
luma = 0.299 R + 0.587 G + 0.114 B
Green carries most of the weight because it carries most of human brightness vision — which is why a photo that looks right on screen can engrave too dark or too light if only its red or blue was strong. The app works in that single channel, with the burn threshold at mid-scale (black below 128, white above) and its error buffer left unclamped, which keeps tone alive in the shadows and highlights instead of clipping them.
Dither: the four kernels by name
The beam burns or it doesn't, so tone has to come from dot patterns — and the app carries the real error-diffusion kernels, named: Floyd–Steinberg (error ÷16, the classic), Jarvis–Judice–Ninke (÷48, smoother), Stucki (÷42, crisper), and Atkinson — which deliberately throws away a quarter of the error at 6 × ⅛, the choice behind its bright, high-contrast look. Bayer 8×8 ordered dithering rounds out the set for an evenly-patterned screen-door texture. Serpentine scanning (the head reversing direction row to row) runs by default, removing the one-way diagonal drift that plain unidirectional scanning prints into faces.
The presets, labelled as estimates
| material | starting preset |
|---|---|
| Light wood | Jarvis |
| Slate · black anodized aluminum · black marble | Stucki, inverted (the beam turns those materials light) |
| White tile | Atkinson |
| Clear acrylic, engraved from behind | Halftone, inverted and mirrored (a 45° screen — the standard single-colour print angle) |
| Grayscale-capable lasers | no dither |
Each preset carries a label worth keeping: "a starting point: try it on a scrap of the same material first." The presets are estimates by admission — the halftone screen's own default of 40 lines per inch is labelled a starting estimate because no laser figure exists for it. Honesty in the settings is part of the tool's design.
And the mask rule underneath it all: only the subject burns. Tap the region, the segmenter keeps what's joined to your tap (a 512×512 pass, the tap as the marker), and transparent pixels never burn — 50% opacity draws the boundary between picture and background.
Engrave a scrap first, always. — the bench crew
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