First of all activate Mental Ray in the Rendering Options.
Create a Physical Sun and Sky system.
Activate Final Gather. At the moment should be enough if you select the Preset Preview Final Gather. It’s just for testing purposes.
Check that the mia_exposure_simple lens shader has been added to the camera. And Check that the gamma is set to 2.2
Launch a render and you’ll realize that everything looks washed.
We need to add a gamma correction node after each texture node, even procedural color shaders.
Connect the texture file’s outColor to the “Gamma Correction” node’s value. Then connect the “Gamma Correct” node’s outValue to the shader’s diffuse.
Use the value 0.455 in the gamma node.
The gamma correction for sRGB devices (with a gamma of approximately 2.2) is 1/2.2 = 0.4545. If your texture files are gamma corrected for gamma 2.2, put 0.455 into the Gamma attribute text boxes.
If you launch a render again, everything should looks fine.
Once you are happy with the look of your scene, to do a batch render you need to put the gamma value of the lens camera shader to 1.
Under the quality tab, in the framebuffer options, select RGBA float, set the gamma to 1 and the colorspace to raw.