Engraved photos.
The prep that decides the burn: interval, tone, dithering — and the presets that admit what they are.
Resolution: the interval decides
An engraved photo's resolution comes from the line interval — the spacing between scan lines. Pixels = size ÷ interval, and DPI = 25.4 ÷ interval. The app's default is 0.1 mm = 254 DPI, right inside LightBurn's suggested 120–300 DPI window (0.08–0.2 mm). Below 120 DPI faces soften; above 300 the beam's spot can't resolve the extra lines anyway.
Tone → ink: the luma
Colour photos become one grey channel by ITU-R BT.601's weights — green dominates what the eye sees:
luma = 0.299 R + 0.587 G + 0.114 B
Shrinking a photo averages areas; enlarging uses bicubic interpolation. The burn threshold sits mid-scale: black below 128, white above — and the error buffer stays unclamped, which keeps tone detail alive in the shadows and highlights.
Dithering: four real kernels
A laser burns or it doesn't — tone comes from dot patterns. The app carries four error-diffusion kernels, each by name: Floyd–Steinberg (÷16), Jarvis–Judice–Ninke (÷48), Stucki (÷42), and Atkinson (6 × ⅛ — it deliberately drops a quarter of the error, the classic bright-look). Plus Bayer 8×8 ordered dithering for a screen-door look. Serpentine scanning is on by default: it removes the one-direction diagonal drift.
The presets, and their honesty
| material | starting preset |
|---|---|
| Light wood | Jarvis |
| Slate · black anodized aluminum · black marble | Stucki, inverted (the beam turns these light) |
| White tile | Atkinson |
| Clear acrylic, engraved from the back | Halftone, inverted and mirrored (45° screen) |
| Grayscale-capable lasers | no dither |
Each preset carries the app's own label: "A starting point: try it on a scrap of the same material first" — they're labelled as estimates until each has a measured source.
Only the subject burns
Tap the subject and Google's MagicTouch model segments it — a 512×512 pass, the tap as the marker, 50% probability to count, and only the region joined to your tap survives (a tap picks one object, not everything in frame). Tap a showing part to keep it; tap an erased part to bring it back. And the hard rule underneath: transparent pixels never burn — at or above 50% opacity is picture, everything else is background.
The halftone screen angle is 45°, the standard single-colour print angle; its default 40 lines per inch slides 10–120 and is labelled a starting estimate — no laser figure was found for it.