Invert brightness for transmitted light
A lithophane uses material thickness to control how much light passes through. Bright image areas should be thinner and dark areas thicker. The lithophane mode therefore reverses the brightness-to-height relationship while retaining a positive minimum base everywhere.
Material changes the result
The same millimeter thickness can transmit very different amounts of light in different filaments, colors and print settings. The tool cannot infer that optical response from the picture. Print a small stepped sample in your intended material and evaluate it with the intended backlight before committing to a large panel.
Check orientation and support
The generated model is a flat closed panel. Your slicer, printer and material determine whether to print it vertically or flat and whether support or a frame is useful. Confirm adhesion, stability and thin-region toolpaths. A valid STL alone cannot guarantee a successful physical print.
Translate brightness into a thickness range
Choose Flat lithophane and begin with a small trial panel. With a 1.2 mm base and a 3 mm additional range, pure white becomes 1.2 mm thick and pure black becomes 4.2 mm thick. Mid-gray is approximately halfway between them. These are geometric values; light transmission through a real print is not linear with thickness.
Keep the backlight, filament, extrusion settings and viewing distance the same when comparing tests. A change in light source can make a previously acceptable panel look washed out or too dark even though the STL is unchanged. Adjust the thickness range from a physical test rather than relying on the shaded mesh preview.
Inspect thin and thick regions before a full print
Check the sliced minimum-thickness areas for continuous paths, and confirm that the thickest regions remain within the intended overall size. Use the processed height image to spot clipped highlights or lost facial detail. The exported panel has no automatically generated frame, curved wrap or hanging fittings. Add any support structure as a separate design step and verify it does not obscure the intended illuminated area.