Choosing Photos That Make Good Lithophanes

Thickness Is Brightness

The principle is simple and it explains every constraint that follows. Thin plastic lets more light through and reads as bright; thick plastic blocks light and reads as dark. A lithophane is your photograph inverted into a height map.

Typical thickness runs from about 0.8 mm at the brightest points to 3 mm at the darkest. That is the entire dynamic range available — roughly a 4:1 ratio in transmitted light, against the many thousands to one a screen can show.

Everything else in this article follows from that number. A photograph with subtle tonal separation has nowhere to put those distinctions, so they collapse into flat plastic.

What Makes a Good Source Photo

The photographs that work share a few properties, and they are not the ones that make a good print on paper.

• Strong, simple contrast. A clearly light subject against a clearly dark background, or the reverse. The eye should be able to describe the image in two or three tones.
• A single dominant subject. One face, one pet, one building. Lithophanes have no colour to separate objects, so a busy scene becomes visual noise.
• Even lighting on the subject. Harsh directional light creates blown highlights that print as uniformly thin plastic — detail already lost before conversion.
• Uncluttered background. Anything behind the subject competes with it. A plain wall or open sky is ideal.

Portraits taken against a bright window are a reliable success: the face is well lit, the background is uniformly bright, and the separation is unambiguous.

Photos That Will Disappoint

Equally worth knowing, because these look fine on a phone and fail in plastic:

• Low-contrast images. A grey cat on a grey sofa. There is not enough tonal range to reproduce, and the print comes out as a featureless slab.
• Very dark photographs. Night shots compress into the thick end of the range, so almost no light passes and the whole panel reads black.
• Images that depend on colour. A red flower against green leaves has striking colour contrast and almost no brightness contrast. Convert it to greyscale before deciding — if it disappears there, it will disappear in plastic.
• Fine repeating detail. Hair strands, fabric weave, distant foliage. Below roughly 0.4 mm of printed feature, detail simply is not resolved.
• Heavily compressed or upscaled images. JPEG artefacts and AI upscaling halos become physical bumps.

Cropping and Resolution

Crop tight. A lithophane is typically 100–150 mm across, and every millimetre spent on background is a millimetre not spent on the subject. Portraits almost always improve from a crop closer than feels natural on screen.

Resolution requirements are lower than people expect. The printed resolution is limited by nozzle width, not pixels — at 0.4 mm per feature, a 150 mm panel resolves at most a few hundred meaningful samples across. Anything beyond roughly 1500 pixels wide adds nothing.

This cuts both ways: a 400-pixel image from a decade-old phone is often perfectly adequate, while a 6000-pixel raw file gains you nothing and slows the conversion down.

Match the aspect ratio to the frame or stand you intend to use, and do that crop before conversion. Stretching a finished lithophane to fit is not an option.

Backlighting Decides Everything

A lithophane viewed in reflected light looks like a slab of textured plastic. It only becomes an image when lit from behind, and the quality of that light matters as much as the print.

Use diffuse, even backlighting. A bare LED behind the panel creates a bright hotspot and dark corners. A frosted diffuser, a light panel, or simply a few centimetres of air between LED and lithophane spreads the light and evens the result.

Warm white generally flatters skin tones; cool white gives crisper apparent contrast on architecture and landscapes. Both work — it is worth testing before gluing anything together.

Print in white or natural filament. Coloured filament tints the transmitted light and reduces the effective range, and dark filament blocks so much that the bright end never reaches bright. Matte white PLA is the usual choice because it diffuses light within the material itself, softening the layer lines.