Materials and Lighting: September 2013

GI/AmbOcc/FG workflow

optional: attache a MR physical light shader to the light. This approximates physical lighting through the value of the light's color. A way to derive an accurate value setting is to divide the photon intensity of the light by PI (3.14).
optional: attache a mia_exposure_simple node (under Mental Ray lense shaders) to the camera(s) you are using to render. This will enable fine-tuned exposure control for your lighting.

Increase Photon Intensity until you can see the image or have the brightness near what you want.
If the Photons hits are splotchy (and they will be) increase the number of GI Photons emitted.
Raise the Accuracy by 200 until you can't see much difference. Go back to the lower setting when you couldn't see a change.
Is there enough detail, or is it looking soft and blurry? If too soft, increase the number of photons.
Use the map visualizer to see how the photons are hitting in the scene. Adjust your light source? Add in additional lights?
Adjust gain and compression in the mia_exposure node
Use MIA_material and enable ambient occlusion.
You might now need to decrease your Photon Intensity (because you now have more photons illuminating the scene).
Again, raise accuracy by 200 until you can't see much difference.
Repeat until satisfied.
If you decide to add in Final Gather to help smooth out results:
- Turn on Precompute Photon Lookup in RenderSettings>IndirectLighting>Final Gathering Map.
- Try immediately decreasing by 1/2the number of Photons emitted . You probably can get by with less and this will save you render time.
- You may want to increase the Photon Intensity so its effect is still evident.
- All the normal Final Gather attributes come into play now and need to be tweaked.
- With Global Illumination turned on, Final Gather will not use "Secondary Diffuse Bounces" Keep that at zero.

Materials and Lighting