A lithophane is a thin relief where dark pixels print thick and bright pixels print thin, so the picture appears only when backlit.
Convert an image to STLImage to lithophane conversion is a thickness problem, not a colour problem. The tool reads the brightness of every pixel and turns it into a height on a thin panel, so the picture only appears when light passes through it. Dark pixels print thick and light pixels print thin. Hold the finished panel against a lamp and the greys become the image. There is nothing to model by hand and nothing to paint.
Who lands here: someone with a photograph, a scan of a drawing, or a logo on a phone, who wants a flat panel that glows when backlit. You do not need modelling software. You need one file, a slicer, and a printer that can hold a 0.08 mm layer. If you have ever printed a flat coaster and wished it showed a face, this is the workflow that gets you there.
Three things happen between an uploaded file and a printable mesh.
Every pixel is sampled for luminance and mapped to a Z value between your minimum and maximum thickness. A bright pixel gets a small Z, a dark pixel gets a large one. What comes out is a height field the width and height of the source image.
A lithophane works by transmission, not reflection. Thick plastic blocks light and reads dark; thin plastic passes light and reads bright. The converter deliberately reverses the usual heightmap logic so the shadows become the tallest part of the panel.
The height field is closed into a mesh with a flat back face and exported as STL. That file holds triangles only, so import it to your slicer and set the orientation yourself: the panel prints standing up, not lying flat.
Five moves, from choosing the file to switching the light on.
Portraits, buildings and moon shots convert well because they have obvious light and dark areas. Flat logos and line art turn into flat plates unless you add gradients first. Crop tight, drop busy backgrounds, and use at least 600 pixels across the shorter side.
0.8 mm minimum to 3.0 mm maximum suits a 0.4 mm nozzle on most FDM machines. Widening the range adds contrast but pushes the thin end toward light leaks. Narrow it for large panels and you keep the blacks readable.
A panel around 100 mm wide with a 3 mm base is a safe first attempt. Keep the aspect ratio locked so faces do not stretch. Print a small test panel first if the picture matters; it costs a few grams and tells you whether the tone range works.
Stand the panel on its long edge: layer height 0.08 to 0.12 mm, 0.4 mm nozzle, 100 percent infill, two or three perimeters, zero top and bottom skin, and a brim for grip. Slow the outer wall to around 30 mm/s. A flat panel needs no supports.
Print in white, natural or clear filament; dark and glossy colours kill transmission. Hold the panel against a window, an LED light panel or a phone screen, then move it a few centimetres back until the image resolves. Too close and the light source itself shows through.
Thickness is the whole contrast budget. Under about 0.6 mm the panel leaks light everywhere and thin walls can fail mid-print; past roughly 4 mm the thickest areas stop passing enough light and the dark end of the image flattens into a silhouette. A 0.4 mm nozzle also caps horizontal detail: features narrower than about 0.4 mm merge. Layer height sets the vertical steps in tone, so a 0.2 mm layer gives visible banding in smooth gradients. Print at 0.08 mm to 0.1 mm when the picture has soft skin tones.
The output is geometry only. STL stores triangles, so no colour and no texture travel with the mesh; a colour lithophane is a printing trick, not a file format. You get colour by swapping filament at a set layer, stacking cyan, magenta, yellow and white panels, or mounting the print over coloured light. Expect the converter to give you one grey height field. Busy JPEGs with heavy compression turn noise into bumps, so clean the source first, and note that a transparent PNG background becomes a flat region at minimum thickness.
Vertical prints are the awkward part. A 120 mm tall panel standing on a 3 mm edge has a small footprint and a high centre of gravity, so add a brim, slow the first layer, and keep the printer out of drafts. The part is solid, so the job takes a long time at 0.08 mm layers. Files are capped at 20 MB, and JPG, PNG, GIF, BMP, TIFF, WebP, SVG and HEIC all upload; resize very large images first.
Upload the picture, set the thickness range, and download the STL. The basic conversion is free, runs in the browser, and needs no account or install.
Convert it into a lithophane: a thin panel whose thickness follows the brightness of each pixel. Print it standing upright in white filament at a fine layer height, then backlight it. The picture appears only when light passes through, not in ordinary room light.
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