In Maya 2014, if you open a scene from a previous version of Maya that renders using the mental ray for Maya renderer, your sampling settings are changed to use Unified Sampling. Some features, such as contour rendering, are not supported with Unified Sampling.
To render legacy scenes with their previously-saved legacy sampling settings, select the Legacy Sampling Mode or Legacy Rasterizer Mode in the mental ray Render Settings: Quality tab. The commands: setAttr "miDefaultOptions.miRenderUsing" 2; (Legacy Sampling Mode) and setAttr "miDefaultOptions.miRenderUsing" 1; (Legacy Rasterizer Mode) can also be used to revert to legacy mode.
New presets are also available for Unified Sampling from the Render Settings Presets menu, including: Preview, Production, FinalFrameEXR.
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