Ambient Occlusion of 3ds max

Ambient Occlusion is an important element of CG as it can noticably raise reality of pieces. It is used for soften the shadows that fall on corners of objects.

Create a mental ray material. Put Ambient/Reflective Occlusion into the surface slot. Then, edit the parameters of AO. Adjust the number of samples. The higher the value, the better the quality. It's important for you to adjust the max distance. It determines how deep will the AO pass be rendered. Put a suitable value into it. The material is done. Open the Render Setup window. Enable Material Override which is below the Processing tab. Drag the mental ray material into the Material Override slot. Choose Instance. Make sure that you have turned off GI, FG and exposure before rendering the pass. Click Render.

After the AO pass is rendered, you need to composite the pass with the original render manually. This can be done with Photoshop. Add two layers and put the AO pass onto the top layer. Adjust the opacity of the AO pass. If the opacity is too high or too low, opposite effect will be resulted.