User Guide > Rendering and Render Setup > Rendering > Appendices > Appendix G: mental ray
user framebuffers >
mentalrayUserBuffer
node attributes
Beginning Maya 2009, user framebuffers are deprecated and multi-render passes should be used instead. User framebuffers are still supported for backward compatibility but for new scenes, they are replaced by the Custom Color render pass. You can use a writeToColorBuffer shader in your shading network in order to direct any output from any shader into a Custom Color render pass. See Multi-render passes for more information.
This option causes mental ray for Maya to interpolate sample values between two known pixel sample values. If interpolation is turned off, the last sample value in each pixel is stored, and pixels without samples get a copy of a neighboring pixel. When this option is turned on, the resulting image has a higher quality, but takes more time to process.