The iray ^® renderer by mental images ^® creates physically accurate renderings by tracing light paths. It requires little setup compared to other renderers.

The principal approach of the iray renderer is time-based: You can specify the length of time to render, the number of iterations to compute, or you can simply launch the rendering for an indefinite amount of time, and stop it when you are satisfied with the appearance of the result.

Early iterations of the iray renderer appear more grainy than the results from other renderers. The graininess becomes less apparent, the more passes you render. The iray renderer is especially good at rendering reflections, including glossy reflections; it is also good at rendering self-illuminating objects and shapes that cannot be rendered with as much precision in other renderers.

A scene rendered by the iray renderer, with the default time of 1 minute

The same scene after a longer rendering time

The same scene after an extended rendering time

A graphics card with a CUDA-enabled Graphics Processing Unit (GPU) will improve the performance of the iray renderer (CUDA stand for Compute Unified Device Architecture). However, the result is not the same as hardware viewport shading: The computation carried out by the iray renderer is physically correct, and the result of a hardware-assisted iray rendering is the same as the result when you render using the Central Processing Unit (CPU) only.

A rule of thumb for GPU usage is that one gigabyte (GB) of memory can store 5 to 10 million triangles (5–10M) of geometry. If textures (usually shared among face triangles) can also fit into GPU memory, that improves rendering performance as well.

The performance of a ray-tracing renderer such as the iray renderer is relatively independent of how complex the scene geometry is. The complexity of light paths is more important: A candle in a labyrinth, or light rays diverging from a narrow window, will take longer to yield a good-quality rendering than light shining through a broad skylight or picture windows. As with other renderers, performance is also proportional to the resolution of the rendered image. The complexity of materials in the scene also affects performance: The more textures, blending, and noise a material has, the longer it takes to calculate the results.

Additional Capabilities and Restrictions

The iray renderer has some additional capabilities and restrictions:

Feature	Capabilities and Restrictions
Geometry	The iray renderer can render all renderable geometry, including mr Proxy objects. It supports Displacement mapping. It also supports camera-based (Multi-Pass) depth of field; in fact, the depth-of-field effect does not increase render time. Geometry is always shadow-casting.
Lights	Lights must be photometric. This includes mr Sky Portal, mr Sun, and mr Sky. The iray renderer ignores all shadow settings for lights. Shadows generated by the iray renderer are always physically based: Lights always cast shadows, and those shadows are raytraced. For the mr lights, the iray renderer also ignores the Indirect Illumination settings. For mr Sun, it ignores the Sun Photon settings and Aerial Perspective; the Sky Model must be Haze-Driven.
Exposure Control	Must be mr Photographic Exposure Control.
Rendering Effects	The iray renderer does not generate G-buffer data, so it can not use render effects, including atmospheric effects.
Render To Texture	Not supported. 3ds Max displays a warning to this effect.
Material Editor	If you choose the iray renderer to render sample slots, it will not render a sample slot background. TipUsing the iray renderer for sample slots can slow performance. Usually the mental ray renderer is a better choice for sample slots.
Panorama Exporter	Not supported
Video Post	Not supported
Lighting Analysis (3ds Max Design)	Not supported
Object Properties settings	The iray renderer ignores these, but the Renderable and Visibility properties are passed to the renderer by 3ds Max, so these settings work as expected.
Batch Rendering	Supported
Command-Line Rendering	Supported
Backburner	Supported

The iray Renderer and Self Illumination

The iray renderer is good at handling self-illuminating materials. In fact, you can render a scene with self-illuminating materials only, and no lights.

TipTo render a scene using self-illuminating materials alone, add a single light object to the scene, and then turn the light off. (If there is no light object in a scene, 3ds Max adds default lights for viewport shading and renderings.)

In an iray rendering, self-illuminating materials can cast shadows, hotspots, and ambient light.

Luminaire Objects, Self-Illumination, and the iray Renderer

In an interior scene (and many architectural exteriors), often you combine a 3ds Max light object with light-fixture geometry that models the lighting instrument itself. The Luminaire Helper Object is a good example of this. You assign a self-illuminating material to the bulb or lamp of the lighting instrument, or to the light-transmitting surface that covers the bulb.

With other renderers, the self-illuminating surface simply appears to glow, while the light object does the actual light casting. But because the iray renderer uses self-illumination as real illumination, a self-illuminating material generates lighting along with the light object: The effect is "double illumination"; the larger the self-illuminating area, the more noticeable the effect.

The reason for this effect is that light-tracing renderers such as the iray renderer don't distinguish between types of rays: Light rays, reflection rays, and shadow rays are all treated in the same way.