Bas-relief, high relief, sunken relief and lithophanes: what is the difference?

These terms are often confused because all four techniques turn a flat image into an object with depth. Their geometry, manufacturing methods and source-image requirements are different, however. Choose the wrong format and a model that looks impressive on screen may be unsuitable for machining, printing or lighting.

A quick comparison of four relief types

Which type should you choose for CNC?

A 2.5D bas-relief is generally easiest for a three-axis router. The tool moves along X, Y and Z but does not machine a complex reverse side. The model should sit on a flat base, avoid inaccessible undercuts and retain its small features after the overall height is limited.

High relief can also be machined, but deep areas require a longer cutter, more passes and careful tool-access planning. Sunken relief is appropriate when you need an incised design or a negative for later moulding.

Which type should you choose for 3D printing?

For FDM printing, a moderately deep bas-relief with sufficiently broad lines is the most forgiving. Place its flat side on the build plate and it can often print with few or no supports. High relief is more likely to need supports and develop defects beneath overhanging features.

A lithophane is printed in light-coloured plastic. Image quality comes from physical thickness rather than surface texture: thin zones transmit more light and thick zones transmit less. A regular grayscale image therefore needs to become a height map, not simply be applied to the surface as a picture.

Practical next step: Create an STL from an image

How to prepare the image

For a relief, choose a source with a clear main subject, readable outlines and distinct depth planes. Portraits benefit from soft light without blown highlights; ornaments need clean contrast; logos work best from a vector or solid-colour original.

The background should not compete with the central subject. Numerous small leaves, flyaway hairs or highlights can become noise in a generated depth map. Before processing, remove the background, improve local contrast and decide which elements genuinely need to become geometry.

Example: a family portrait for a wooden plaque

For a portrait on a keepsake-box lid, choose bas-relief rather than a lithophane. First separate the people from the background, create a moderate depth map, add a level base and limit the total height. After exporting the STL, open it in CAM software, select the cutter size and check that eyes, hair and clothing folds survive at the chosen scale.

Practical next step: Inspect a model in the STL Viewer

Common mistakes and limitations

Do not call every dimensional image a bas-relief. A full 3D figure flattened along one axis often produces distorted faces and awkward undercuts. A lithophane is not a substitute for a relief plaque: without backlighting it has little contrast. When making a mould, confirm whether you need the positive relief or its negative.

Frequently asked questions

Conclusion

Choose the relief type by the physical result: bas-relief for raised decoration and CNC, sunken relief for an incision or negative, high relief for a strongly sculptural form, and a lithophane for transmitted light. AIPRINTGEN can turn a photo into a relief STL model, which you can then check for size and manufacturability in a slicer or CAM package.

Practical next step: Open the bas-relief generator