I don’t use the gray scale depth map directly. I first convert it to an STL using Heightmap2STL download | SourceForge.net.
Usage: filename model_height base_height
java -jar heightmap2stl.jar celtic-design-grayscale.png 1 0
In Model Size
uncheck Unlock Lock XYZ
Change X and Y to your material, and Z to the max thickness you’ll be carving.
Zero Plane I set to some small fraction less than my thickness to trim the polys from the bottom plane.
I’m sure you know how to work the 3d roughing and detail toolpaths.
Let me know if you have more questions.