Issue: Volume: 23 Issue: 11 (November 2000)

Mental Ray 2.1

By George Maestri

Mental Images' Mental Ray has always been one of the most beautiful rendering solutions on the market. It is also one of the most technically adept renderers available, offering users the ability to program custom shaders, much as they can with Pixar Animation Studio's Render Man. But unlike RenderMan, which is strictly a scanline renderer, Mental Ray is a raytracer, which gives it a definite advantage when creating reflective and refractive materials. Version 2.1 of Mental Ray adds a number of new features, including global illumination, caustics, and a port to an additional program.

In the entertainment market, Mental Ray has been closely allied with Softimage, which has exclusively bundled the software for a number of years. With version 2.1, however, Mental Images has broadened its market by offering the software as a plug-in for Discreet's 3D Studio Max 3.1. This represents a big move for both Mental Images and Discreet, as it gives 3D Studio Max the top-quality rendering it needs, and offers Mental Images a much bigger user base to sell to. This review focuses mostly on the 3D Studio Max port; however, all the rendering features described here are available for all versions of Mental Ray.
Mental Ray's caustics capability allows for the accurate depiction of water and for the realistic reflections that scatter off of the walls in the room.

Installation is fairly straightforward. However, the Max version has an odd serial port dongle, so you need to make sure you have a free serial port on your machine. Softimage's port of Mental Ray keys off of Softimage's parallel port dongle, which is a more convenient setup.

The connection to 3D Studio Max is accomplished through a series of plug-ins that are installed a long with Mental Ray. The interface is for the most part transparent. Shaders are built within Max's material editor, much the same as with regular Max materials. All of Max's shader and material types are supported, with the exception of the Strauss shader and the Morpher and Raytrace materials (because Mental Ray already supports raytracing, the exception of Raytrace materials is not a big issue). Mental Ray also does not support .JPG files as bitmaps. These exceptions are minor, however. I found it easy to build new shaders as well as convert existing scenes using Mental Ray. If you know how to build a Max shader, you can build a Mental Ray shader.

Of course, Mental Ray provides a number of features not found in the standard Max renderer. The most intriguing new feature in Mental Ray 2.1 is the addition of global illumination, which enhances the realism of a scene by simulating the inter-reflection of light. Although not a true radiosity renderer, global illumination generates such radiosity-like effects as "color bleeding," in which, for example, a white shirt next to a red wall will appear to have a slight red tint. A globally illuminated scene also generates much softer and more realistic renderings than a raytraced scene.

Another feature closely related to global illumination is caustics, which simulates the effect of light reflected off of or refracted through another object. This effect is apparent in the simulation of surfaces such as water, which changes its light-scattering properties as its surface changes. In Mental Ray, both caustics and global illumination are accomplished through the use of photon mapping, which simulates photons of light traveling through a scene, being reflected or transmitted by objects. When it strikes a surface, the photon is stored in a photon map.

Of course, all this realism comes at a cost. Generating photon maps is time consuming. To improve performance, you must explicitly specify to Max which lights and objects emit photons for caustics and indirect illumination. To further reduce the time required to generate a photon map, you can limit the number of times a photon can be reflected, refracted, or both.

Mental Ray's depth-of-field capability is robust and produces realistic and smooth depth of field without the edge artifacts that can crop up when using Max's own depth-of-field capability. This feature is based on a real-world camera analogy, with the camera's f-stop controlling the amount of blurring. This is very helpful for those trying to match cameras with real-world footage.

In short, aside from minor limitations such as the extra hardware dongle and the lack of support for Max's Strauss shader and Morpher materials, Mental Ray has a number of excellent enhancements that keep it at the cutting edge of rendering technology. What's more, it produces beautiful images. Any Max user who tries out Mental Ray will probably not want to go back to the old Max renderer again.

George Maestri is a writer and animator living in Los Angeles.

Price: $2995. Network licenses available.
Minimum system requirements: Windows NT/2000, Unix, Linux, Irix, SunOS, IBM AIX, or HP-UX. See Web site for supported hardware/software combinations.
Mental Images
Berlin, Germany
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