Image to lithophane

From plain Rec. 601 luma computed at each sampled point, ignoring the alpha channel entirely, then mapped between thicknessMax at the darkest pixel and thicknessMin at the brightest, since light passes more easily through the thin, bright areas of a lithophane.

thicknessMin sets the thickness at the brightest pixel in the photo, 0.6 by default; thicknessMax sets the thickness at the darkest pixel, 3 by default, and it has to be greater than thicknessMin or the tool refuses.

How many grid samples run along the longer axis of the image, from 8 up to 512, 128 by default. A higher resolution keeps finer detail from the photo at the cost of a larger, heavier file, since every extra sample adds more triangles to the mesh.

It swaps which end of the brightness scale is thin, so dark pixels become thin and bright pixels become thick instead of the standard lithophane convention.

Yes. The top bumpy surface, a flat bottom and four side walls are all stitched together into one watertight solid, verified during development by running the tools own output back through the same watertight check Check a 3D model for 3D printing exposes.

STL or GLB, set with format, STL by default; the file is named after your photo with a -lithophane suffix.