Many users have noted unexpected results when using the RPC Environment with a Mental Ray Daylight System. This is primarily because of the way that Mental Ray blends colors. There is a large sky texture that is some shade of blue and a ground plane that is brown or green. The effect of the blending of these two becomes a murky brown/green where blue should be. Through a little trial and error I have created a settings formula that works nicely with most scene configurations.
When the RPC Environment is added to a scene with a Mental Ray Daylight System it will render something like this:
RPC Environment with Mental Ray - Default Settings
This looks nothing at all like the rendering results with the scanline rendering. I will show you how to fix this.
We will start by changing the Physical Scale values under the Environment and Effects panel. I have changed from Physical Units to Unitless and changed the value from 1500 to 90,000.
Physical Scale set to Unitless 90,000
This gives us the following results:
Rendering results with new Physical Scale
There isn’t much change shown, but when we make the next modification it will be apparent. Go into the RPC Mass Edit Dialog and change the Self-Illumination value from 0 to 55.
Mass Edit Dialog Self Illumination
Now the RPC Environment’s color will render much better.
Rendering with New Values Applied
Finally the sky looks more blue than green. To make it look even better I will brighten the scene by boosting the exposure value from 15 to 14 (lower values increase brightness). This will give us a rendering that looks like this:
Rendering with New Exposure Control Value
Utilize the exposure controls to tweak your rendering even further.
I hope this tip helps and good luck with your next rendering.