I experience a problem with the sun light which I do not quite understand, maybe somebody here can help:
Very very slight sloped grounds reflect too few sun light when comparing to flat grounds.
In this image:
there is a very very dark grass patch at the far end to the right at the hedge. This is much darker than expected. The slope has an angle of 1.77° and goes down to the right. To compare a non-sloped flat ground, see the rectangular strip which extends from the resting young people to the hedge. To the left of this strip, we have a similar slope into the other direction. The photo was rendered at 13:30h in summer.
I was expecting the amount of reflected light to depend on the scalar product of surface normal vector and light direction, but what I see here is odd. What's happening here? Why affects a slight variance the object's brightness so much? It's not a texture problem, solid green color (matt surface) shows the same strange result.
