How image-based lighting (IBL) works

When an IBL node is created one or more of the following mental ray for Maya shaders is used:

Environment Shader

Along with Final Gathering this shader implements classic style image-based lighting. The color of the environment is picked up by final gather rays and incorporated into surface illumination. An environment shader is passive. It doesn’t actively contribute to the scene’s lighting; instead, it gets sampled only as needed. Best results are achieved if the IBL texture is diffuse. A specific case would be a texture consisting of a single color; this results in ambient occlusion computation.

Photon Emission Shader

Photons are emitted from the IBL environment sphere. These photons pick up their energies (or colors) from the IBL texture. A photon emission shader emits all its photons once per frame. It is more active than an environment shader in this sense. Photons work best with mostly diffuse IBL textures.

Light Shader

A low-resolution control texture is computed (from the file or procedural IBL texture) and mapped to the IBL environment sphere. Whenever direct lights are sampled, the light shader is invoked. In this sense, the light shader approach is the most active one, and the most expensive. The IBL environment can be seen as one big area light. This approach works best (also due to importance sampling) if the IBL texture contains sharp features, and preferably contains many more black than non-black pixels.

These three approaches may be combined to achieve specific effects, at the expense of computation time.

To use image-based lighting

1. In the Indirect Lighting tab of the mental ray tabs of the Render Settings Window, click the Create button beside the Image Based Lighting (IBL) attribute in the Environment section.
2. A new IBL node is created, replacing any currently connected node. (Though multiple IBL environments can exist in a scene, only one can be used at a time.)

   The IBL manipulator tool appears in the scene view, and the IBL node’s Attribute Editor automatically pops up.

3. Set the IBL node’s attributes.

   For details, see Image based lighting node attributes.

4. Position the IBL node with the IBL manipulator tool.

   For details, see Position an IBL texture.

5. Render with Final Gather or Global Illumination to illuminate the scene.

   Final gathering picks up incandescence samples from the environment texture. Illumination models deal with these samples similar to direct light arriving from, for example, a spot light.

   Note

   • IBL environments can be previewed interactively (if they are File texture based).
   • Maya's environment shaders do not work well with IBL. IBL provides UV coordinates to the attached shading network, but Maya’s environment shaders do not base their calculations on UVs. Maya environments are supported with final gather-based IBL, but photon and light emission are unsupported.

Position an IBL texture

When you create an IBL node, its shape is represented in the scene view.

Moving (and to a certain extent scaling) the shape has no effect because the environment is considered infinitely distant. For best results, scale the shape as large as your clipping planes permit.

Rotations, however, let you position the texture on the IBL node shaders.