Clay Render Mental Ray (3DS MAX)

Picture 1. Clay render with Mental Ray in 3DS MAX.

27.08.2007 Category: 3D (Rendering)
Incomplete models (wip) are often rendered with a clay render technique. Clay render means a rendering which looks like a picture of a clay model. In this tutorial I cover a clay render technique in 3D Studio MAX using Mental Ray renderer. If you are not familiar with the clay render concept I encourage you to first read about materials, background and lighting from my tutorial: Clay Render in 3DS MAX.

Mental Ray Final Gather

Picture 2. Enable Final Gather.

Picture 3. Clay render in 3D Studio MAX with default settings of Mental Ray's Final Gather.

With Mental Ray, clay render can be achieved simply by turning Final Gather on. Turn Final Gather on (picture2) and try to render your image. Picture 3 has been rendered by using the default settings of Final Gather. From picture 3 it's easy to notice a few things that could be improved. The edges of the model are jagged and shadows and shading look grainy in some places.

Sampling Quality

Picture 4. Edges can be made smoother by increasing Mental Ray's sampling quality.

The jagged edges can be fixed by increasing sampling quality of Mental Ray. Sampling is an antialiasing technique. Sampling settings of Mental Ray can be found from Renderer tab from Sampling Quality section. I am not going to go through the sampling settings or mathematics behind them but you can easily increase the sampling quality by increasing Minimum and Maximum values found in Samples per Pixel section. Try for example values 4 and 64 like in picture 4.

Final Gather Basic Parameters

Picture 5. Rendering quality can be increased by adjusting basic settings of Final Gather.

Picture 6. High quality rendering can be achieved by raising Mental Ray's quality settings.

Grainy shadows and shading can be fixed by adjusting Final Gather's basic parameters on Indirect Illumination tab. I am not going to go through the complicated mathematics behind the settings but simply put, you can increase the rendering quality by raising the following values:

• Initial FG Point Density
• Rays per FG Point
• Interpolate Over Num. FG Points

Notice that raising these values affect considerably to the rendering speed. It's a good idea to experiment with different values to find satisfactory rendering quality. The realism of the rendering can be increased by adjusting the following values:

• Diffuse Bounces
• Weight

Diffuse Bounces means the bouncing of the light and Weight affects to the amount of light that is left after a bounce. Picture 6 has been rendered with the following Mental Ray settings:

• Renderer > Samples per Pixel
  • Minimum: 4
  • Maximum: 64
• Indirect Illumination > Basic
  • Initial FG Point Density: 40
  • Rays per FG Point: 250
  • Interpolate Over Num. FG Points: 27
  • Diffuse Bounces: 1
  • Weight: 0,4

Notice that when Initial FG Point Density is raised this high, the rendering might took a long time. Intel Core 2 Duo E4300 rendered picture 6 (400 x 300) in about three minutes.