Preview Overrides:

Using the Preview buttons at the bottom left of the RPM UI is a quick and easy way to preview single frames of your pass setup.

Often though you do not need a full size or full quality render, so to facilitate efficient use of your setup time RPM allows you to turn off some features of the renderer and also render a reduced size image for quicker feedback. The 'Preview' tab in the RPM interface will display the Preview Overrides controls.

Within this rollout there are some general override settings - such as image size - as well as renderer-specific controls for the most common renderers, ie: 3dsmax Default Scanline, Mental Ray. Brazil/Rio, Vray and FinalRender Stage-1. The rendering parameters that you can disable or set to lower sampling rates depends on the renderer, but it is features such as Antialiasing, GI, GI sampling, DOF, DOF sampling, shadows, mapping, motion blur, etc.

Preview Overrides need to be enabled in the Preview Setup rollout to affect the previews created with RPM, there is a checkbutton at the top left of the rollout. The on/off state of this is displayed in the name of the Preview group at the bottom left of the RPM UI, the group title will read either 'Preview: O'rides OFF' or 'Preview: O'rides ON' making it easy to see before you preview if the overrides are enabled or not.

Quicktime Movie demonstrating using preview overrides with Mental Ray. 982k (zip 209k)