Terrain generation - multiple gradients Thread

Hi,
This is my first post here, so HELLO @ ALL!
Not sure if this is the right place for my problem, so, if I'm wrong here please move the thread to the right place.

I'm trying to make a new map for a game called 'FarmingSimulator 2011'.
Now I'm starting with the terrain, and there is my first problem. The game comes with a Level Editor an it is obviously intended to create the terrain manually with this editor. Anyway, the terrain is based on a .png-file and one can edit the terrain with this file,too.
But the way how the terrain is generated from the png confuses me somehow.
The editor reads the altitude from the red channel, and smoothes it with the green channel - means it interpolates between two red-values with a green gradient.
I can't explain it better, so here are some pics:

Baaah...can't link images because I'm new here. Please look here: Home.arcor.de

Finally the question: I need a green gradient between each (! 0-255) value of red. Does anyone have an idea how I could do this?