Height map tiling: what is it due to? I'm creating a script that produces height map from a mesh.

Testing it, I remarked strange rounded tiling... so I thought it was a bug in my code (again...), but comparing the result with another map taken from the web, it is similar:

my texture on the left, the web texture on the right:



And the corresponding images:

Mine:



From the web:



These tiles appear only at a given subdivision of the grids and above, not if too low.

What is it due to?
Not sure what is really the underlying cause, but I figured out how to reduce the artifacts.

It seems to be related to the image filtering interpolation method.
Turning on Interpolation and increasing the Filter Size property seems to reduce the effect noticeably.