CGSociety

CGSociety :: Technology Focus
13 May 2010, by Jamie Cardoso

Jamie Cardoso is an author and independent technologist. He volunteered this look at the new mental ray 3.8 and its use in 3ds Max 2011.
The standalone mental ray 3.8 is fully equipped with numerous powerful features such as Iray rendering mode; stereoscopic rendering; IBL mode, etc. However, while some of these new features are not yet fully integrated with 3ds Max, and others are only available via the command line or via plug-ins such as ctrl_ghost_settings.

Importons/Irradiance
Although the ctrl_ghost_settings for 3ds Max 2011 come with additional features supported by mental ray such as Final Gather; Image Based Lighting; progressive rendering; Iray; Ambient Occlusion Cache; etc, most of them are still being optimised, fixed and/or not fully integrated. Currently, the features that users may find quite useful for production are the importons and irradiance particles.

Irradiance Particles: Irradiance particles are collected after the importons are shot from the camera. They preserve the information of both direct and indirect illumination for the rendering process. The direct and indirect illumination information is determined by the number of passes. For production, the importons and irradiance particles can be quite an asset when used simultaneously and cached.

In order to cache the file, the user is required to type in or paste the location/destination to where the file will be saved; followed by its name. The 'interpolate' function also requires it to be set to 'Always'. The first render may take a while to process. However, the subsequent render times will be improved dramatically. It is common practice to cache the file at smaller resolution such as 600x450, and later render it at higher resolution (i.e. 5,000x3,750px).

It is worth noting that when the environment evaluation is cached, its indirect shadows may not be as accurate as otherwise. However, the rendering times may drop by more 75% at times; and its quality will still remain superior to any final gather solution. The render [above] had originally taken over three hours with numerous light sources such as daylight system, mr_sky_portal, photometric lights with final gather cached. That having been said, the same image had taken less than 45 minutes, with daylight system, importons and irradiance particles cached. The IBL file was applied to the 'environment/reflections' shader, of the 'environment/background switcher parameters'.

Color override/ray type Switcher parameters
This fully integrated mental ray shader for 3ds Max 2011 provides users with an array of options to override the eye rays; transparency; reflections; refraction; shadows; final gather; photons and environment. This shader is accessible from the 'material/map browser' dialog box list.

Users may find the following useful:

Eye Rays: Only overrides/replaces the color/texture of the relevant surface. Note that these changes do not affect its surface when reflected from a different object.

To also override its original color/texture when reflected on other surfaces, one is required to copy and paste/ instance the eye rays’ contents onto the 'Reflections' toggle.

When used for surfaces, users often apply the 'object color' and/or the 'Ambient/Reflective Occlusion' shader. It’s worth noting that the eye rays function can also be plugged to the 'environment map' toggle, especially when using IBL files.

Reflections/Refractions: This function only overrides/replaces the color/texture of the relevant surface.

Final Gather: This function only overrides/replaces the Final gather contribution of the relevant surface’s color and/or texture. This function is quite useful to eliminate color bleeding from surfaces.

Photons: This function only overrides/replaces the Global illumination contribution of the relevant surface’s color/texture. This function is also quite useful to eliminate color bleeding from surfaces. As mentioned earlier, all the 'Color Override/Ray Type Switcher Parameters' functions can also be plugged to the 'environment map' toggle, especially when using IBL files.

Kelvin Temperature Color
This newly integrated shader for 3ds Max 2011 helps to boost and define the correct color temperature of a light source, surface color and/or a texture. It’s common practice to plug this shader onto the 'mr Sky portal' custom toggle, in order to be used as a light card for interior scenes independently from a daylight system and/or a 'Skylight' object. This shader can be easily accessed from the 'material/map browser' dialog box list. Followed by dragging and dropping the shader onto one of the “material editor” dialog slots, in order to edit its parameters.

Intensity: This function sets the brightness of the color temperature.

Finally, when used with 'mr Sky portal', it can also help to emulate recessed lighting patterns. The images below clearly depict its results.