POVRay and Height fields and resolution...

[waldronate]

That looks like a basic point-sampled height field. Smooth, rolling terrain from an image is very hard to get good ray-tracing results from because most of the area is flat shelf areas of constant values with a near-vertical step to the next value. The normal goes off an a very different direction at the step and that's what gives the dark area.

Does the smooth heightfield modifier do any good?

[Crayons]

Ah, thanks both of you! (I think).
The example render had the smooth modifier on, without that it's even worse. I've tried converting to a high res triangle mesh from a lower res image but basically I think I'm stuffed, as it were. Ho hum.
Looks like the dither idea will suffice, it'll make the ground look sort of "mole-hilly" !!

Thanks for the suggestions though guys! I might have something interesting to show you soon.

cheers!