Carving photographs and lithophanes
Short answer
Software can read a greyscale image as a height map and carve it as a relief. It works when the image has strong tonal separation and a clear subject, and it fails on busy photographs. The finished carve is read by shadow, so the lighting it hangs in matters as much as the carving.
The two different things people mean
| Photo relief | Lithophane | |
|---|---|---|
| How it works | Brightness becomes height. Read by shadow in reflected light. | Brightness becomes thickness. Read by transmitted light from behind. |
| Material | Opaque: wood, solid surface | Translucent: thin corian, acrylic, or thin light-coloured wood |
| Tonal direction | Bright areas usually raised | Bright areas thin, dark areas thick |
| Viewing | Needs raking light to read at all | Needs a light source behind it |
Which images work
Works
Single subject, clean background, strong contrast, clear light direction
Struggles
Group photos, busy backgrounds, flat even lighting
Fails
Low resolution, low contrast, or anything where the subject blends into the background
The reason is that height maps have no colour. Two areas that are different colours but the same brightness become the same height, and the subject disappears into the background. Converting to greyscale before you start tells you immediately whether the image will work.
Preparing the image
- Convert to greyscale and look at it. If you cannot read the subject in greyscale, the carve will not either.
- Increase contrast so the subject separates clearly from the background.
- Remove or flatten the background, often the single biggest improvement. A carved subject on a flat background reads far better than a carved subject in a carved room.
- Blur very slightly. Pixel-level noise becomes surface texture you do not want.
- Use the highest resolution you have. A 500 pixel image carved at 10 inches gives you 50 pixels per inch of height data.
Carving it
- Z depth is a judgement, not a calculation. Too shallow and it disappears. Too deep and the face looks like a mask. Test on scrap.
- A small ball nose is required, usually 1/16 inch or smaller, and a tapered one for rigidity.
- Fine stepover. Photo reliefs are all about subtle gradients, which is exactly where scallops show.
- Expect a long carve. Small tool plus fine stepover over a whole panel is the slowest combination in CNC.
- Material has to hold fine detail. Close grained hardwood, MDF or solid surface. Open grained wood will destroy the image.
Lighting is half the result
Test the piece under the light it will live in
A photo relief is read entirely by the shadows in its surface. The same carve can look extraordinary lit from one side and like a blank panel lit head on. Before you decide a carve failed, take it to a window or hold a light at a low angle across it. Many disappointing photo carves are actually lighting problems.Further viewing