Help with physical sun and sky

[Anonymous]

I am working on an animation with a bus driving on highly reflective surface in the sunset.

I am using Mental ray's physical sun and sky (PSAS) for lighting the entire scene.
The PSAS with FG creates a nice soft look that I really like. However, the colors of my buss appear a little washed out. The colors appear like they are seen through a white uniform fog. The effect is quite subtle, but not what I am after. I want the yellow of the bus to appear almost golden with nice contrast, not over lit.

I have tried rotating the light. None of the settings of the PSAS seem to make the colors of the bus "pop". The colors look better (but not perfect) if I turn of FG but then other things start looking real bad. I have tried tweaking my materials's diffuse, eccentricity, specular rolloff and reflectivity but can't seem to alleviate the problem that way either. It is as if too much light is coming from the sky.
The bus is driving on a white floor (which I am also unable to get to appear white). The floor takes on the color of the sun and sky because of its reflectivity instead.

Any tips and tricks here would be very much appreciated.

[Anonymous]

I think I have found the problem.

PSAS creates a gray ground plane which is not real geometry. This ground is pretty useless since shadows can not fall on it, nor can it receive reflections. So I had created my own ground plane on top of it. The problem is that the color of PSAS ground plane is still part of the equation despite that it is covered by geometry. Setting the ground color to black did the trick.

[Anonymous]

For the color not to look washed, use a gamma node.
If its just a simple color create a gamma correct node, in gamma put .455, in the value use the color you want or plug your texture there. Then connect the gamma correct node to the disuse slot of your shader.

[Anonymous]

I can't get the gamma thing to work. I just don't see any difference.

I used a bright red color on the gamma correction node. The gamma node has 3 gamma value boxes. Only one of them can be connected to the diffuse channel of my blinn material. so I do that. The color I choose on the gamma node does not influence the color of the blinn unless I simply connect its color to it. Hardly any difference is seen with the gamma connected/disconnected to diffuse.

What am I doing wrong here?

[jamesarndt]

There is a necessary correction that needs to be done when you set up the physical sun and sky. Right after it's created, go into the hypershade and go under the Utilities tab...inside there will be an Exposure node. In it is a setting for Gamma. It will be set to 2.2...you will need to drop this down to around 1.1 or just 1. Should address your gamma issues.

[n8skow]

if you go the gamma node route (for each shader) you need to use the inverse gamma value - .454 (to correct for gamma 2.2) - not an RGB value...

[Anonymous]

Adjusting the gamma in the exposure node works wonders.

I will have to try the individual gamma node trick again using n8skow's reversed value...

[n8skow]

it should be noted that adding an individual gamme node for a image file will only change the appearance of that particular shader - whereas changing the exposure node setting will gamma correct the entire scene...