Ambient Occlusion (AO)
It is common practise to save out the AO as a separate pass, for compositing. This methodology enables users to have full control of its appearance without having to re-render.
Open the "material editor" and choose a completely new material slot by dragging and dropping from one editor slot to another.
Rename it, and load a new mental shader from the "material/map browser" list. See (Fig.30a and Fig.30b)
With the mental ray shader loaded, click on its "surface" toggle to load up the "ambient/reflective occlusion" shader, from the "material/map browser" list.
Its parameters should load up; change "samples" value to 60; the "spread" value to 7.0 and "max distance" to 0.3.
Note that these values worked best for the effect intended however; one may try different values, if desired. (Fig.31a and Fig.31b)
Next, open the "render setup" dialog and select the "processing" rollout.
Enable the "material override" again, and drag and drop the AO material slot to the "material override" toggle. Choose "instance" method. (Fig.32).
Disable the FG and open the "environment and effects" dialog.
Disable the "use map" function and its colour swatch to white. This is to make the background color white.
Keep the image "sampling quality" as before 1/16 samples per pixel ; "Mitchell" filter and the "soft shadows precision (multiplier)" to 1.0 .
Finally, turn off the exposure controls and click render. (Fig.33a and Fig.33b)
Photoshop is very powerful and useful when incorporating quick changes and/or effects that would otherwise be time consuming to address in Max alone. Having said that, it is also important to have relatively decent renders from Max. This work process will later prove very fruitful for one's final piece.
In this final part of the tutorial, we will bring in the main rendered image, along with the pre rendered AO element.
Although we had rendered numerous elements, we will be using the AO pass only, for the purpose of this exercise. Open the main render along with the above mentioned element.
Select the rendered image document; on its "layer" rollout duplicate it, by right clicking and selecting the "duplicate layer" option from the popup list.
Name it "render"
Also, change its original white color to red, by right clicking on the layer and selecting the "layer properties" option from the list. This will help differentiate layers. (Fig.34)