Iray for 3ds Max can render many simultaneous renders elements. These are available for standard Production Rendering, and can also be displayed in ActiveShade mode when using the Iray+ Frame Buffer. These are useful for post-processing and compositing without the need to re-render scenes. They can be found on the Render Setup > Render Elements tab.
For Production Renders, Render Elements are stored alongside your rendered image in the directory set in Render Setup > Common > Render Output. They use the name you have specified in Render Output with the suffix of the render layer name (for example, Myfile01 - Alpha.png). Render Elements can also be saved out from the Iray+ Frame Buffer.
See LPEs if you require more flexibility when creating such extra layers (for example, a purely specular layer).
Alpha: A grayscale alpha channel representing the transparency in the scene. The darker the pixel, the more transparent it is. Black = Totally Transparent, White = Totally Opaque
Depth: A grayscale representation of the depth in the scene. The nearer the object to the camera the whiter the object. Useful for adding depth of field in post-processing
Distance: Similar to Depth, except it measures distance from the camera, so the furthest edges of large objects are further away than the center even though they are the same depth in the scene
Normal: Surface normal, used for shading
Object ID: Assigns each object a separate color. Useful for selecting individual objects in post-processing
Material ID: Assigns each material a separate color. Useful for selecting objects with the same material in post-processing
Diffuse: Renders only diffuse components within the scene
Specular: Renders only specular components within the scene
Glossy: Renders only glossy components within the scene
Emission: Renders only emission components within the scene
Ambient Occlusion: (Iray+ Interactive Renderer only) Renders areas of the scene using Ambient Occlusion.
✱ Note: Diffuse, Specular, Glossy and Emission layers are not available when performing Lighting Analysis.
Distance and Depth
Both Distance and Depth have a finite resolution. If using the infinite Ground plane (Physical Sky or IBL Iray+ light) then the available resolution of the the depth values will be spread over the whole ground plane and so may not give the required results for the main model geometry. Unless viewing a finite portion of the ground plane, it may be best to remove it when rendering these elements.