Why does my photo engrave as one black blob?
A laser has no grey. At a given power it either burns a spot or it does not, so a photo full of mid-tones comes out as a dark mass. The picture has to be turned into something two-toned first, dots or lines whose size and spacing carry the tone, prepared at the exact size and resolution you will burn it at.
What to do to the picture first
- Crop to the subject and raise the contrast: shadows to near black, highlights to near white.
- Resize it to the size you will burn, at the resolution your machine engraves at. Preparing a photo at 4000 px for a 60 mm tag throws away the work.
- Turn it into dots (a halftone) or a dither. Halftone dots survive wood grain better than fine dithering, which can silt up.
- On a dark material, invert: you are burning away the dark surface to reveal light underneath, so the tones run the other way.
Let one of you dither, not both
Laser software dithers images itself. xTool Studio calls it the bitmap mode of an engrave layer, with Jarvis among the choices, and sets the line spacing next to it; LightBurn has the same thing under image mode. That is the software turning your greys into dots as it burns.
So decide where it happens. If you prepare a halftone here, take the SVG: the dots are already shapes, and nothing dithers them a second time into a moiré. If you would rather let the machine do it, hand over the plain greyscale photo, prepared and contrasty, and pick the bitmap mode there.
Material decides how fine you can go
Slate and anodised aluminium hold fine detail. Plywood does not: the grain is a competing pattern and the softer rings burn deeper. On plywood, fewer and larger dots look better than a faithful reproduction that turns to mud.
For a relief rather than a picture
Depth engraving reads a grayscale image as height, not as tone. That is a different preparation: a depth map with the black and white points set so the whole range is used.