Ambient occlusion is very very important to get good object details in multi pass renderings. Let we see how to get good occlusion using mentalray for maya. For this I used a downloaded model, it looks like this in wire frame view.
let us render with default shader Lambert !
Now let us prepare occlusion shader using mentalray utility " mib_amb_occlusion " to get mentalray utilities in hypershade we need to check 'mayatomr.mll' in plug-in manager. as shown in this picture.
let us connect the occlusion utility to our lambert shader
cool now we will render the scene with default settings. the rendered image looks like this.
we got few contact shadows and the image quality is not good. so let us change the render and shader settings like this.
let us render with the modified settings.....
now its better than the previous render, we will render it for more quality and clarity, by adjustig the main shader (lambert) channels. already we connected mib_occlusion utility to the ambient channel. no change the shader color to 1 (h=0 s=0 v=1) and diffuse, translucence, translucence depth and translucence focus to 0. like this....
and the final occlusion render will come like this.
next compositing occlusion pass in FUSION.