How to Use a Depth Map for CNC Carving

What grayscale values mean

A typical 8-bit grayscale image has values from 0 (black) to 255 (white). A CAM height-map importer maps those pixel values across a physical height range that you choose. Which end becomes the high point depends on the software's import setting; some workflows also invert the image. Always inspect the relief preview before creating a toolpath.

Do not assume white is always raised. Confirm the direction in your CAM preview. If the background appears as a peak and the subject as a recess when that is not intended, use the importer's invert option or invert the map, then preview again.

Import checklist

Choose a project size that matches the intended finished carving and stock.
Import the grayscale PNG as a component, height map, or relief using your CAM program's equivalent command.
Set the physical relief height conservatively for the material, cutter, and design. The pixel values alone do not define a safe cutting depth.
Check image orientation, crop, aspect ratio, and whether the CAM software has stretched the map.
Inspect the 3D preview from several angles. Look for inverted relief, abrupt borders, noisy texture, or details that disappear at the chosen size.
Only after the model looks correct, select cutters and generate roughing and finishing toolpaths using settings appropriate to your machine.
Simulate the toolpath and check stock, clamps, cutter reach, and safe travel moves before machining.

Choosing a physical relief height

More height is not automatically more detail. A large height range can make slopes steep and may create narrow regions that are difficult to machine with the chosen cutter. A shallow relief can preserve a soft appearance and simplify finishing, but can make subtle differences hard to see. Start with a scale appropriate to the stock thickness and design, then use the CAM preview and simulation to decide whether the form is readable and machinable.

Tool diameter, stepover, grain direction, material, and machine rigidity all affect the result. A map that looks smooth on screen can still produce visible scallops if the finishing stepover is too large for the desired surface. Conversely, a very small stepover can greatly increase machining time. Use your CAM software's simulation and your established shop settings to balance finish and time.

Edges and borders

Height maps often transition to a flat edge or background. If that transition is abrupt, the toolpath may create a visible wall or ridge. Leave a margin in the image, add a border or blend in CAM when appropriate, and inspect the outer perimeter in the 3D preview. Do not let a border obscure the subject or push the carving beyond the stock.

When to use a depth map versus an STL

A height map is convenient when your CAM software can create a relief directly from an image and you want to control the physical height there. An STL is a mesh with geometry already represented in 3D; it can be useful for mesh-based CAM or a 3D printing path. Choose the format your downstream software handles reliably, and verify scale after import. See the photo-to-STL workflow and the mesh inspection guide.

Before you cut