Image based lighting node attributes

These are descriptions of the attributes in the mental ray IBL (Image Based Lighting) node. See Image-based lighting (sky-like illumination) and also Render infinitely distant (sky-like) illumination and reflection.

In Maya 2015/2016, this feature has been improved to provide higher quality render results at a much faster speed.

Image Based Lighting Attributes

These are the attributes in the Image Based Lighting Attributes section.

Mapping

Select a UV space for the environment sphere: spherical (latitude-longitude) or angular (HDR Shop).

Type

Select whether to map a file or a procedural texture as the IBL texture. File textures can be previewed interactively. See also Texture.

Image Name

Name of image on disk. Click the browse button to browse to the file.

Use Frame Extension

If turned on, the texture's file name may change on a per-frame basis. This is used to load an image sequence instead of a single file.

Frame Extension

The frame extension.

Texture

If Type is set to Procedural, connect a 2D texture shading network to this input.

Infinite

The default value for this attribute is on, and results in the default IBL behavior.

If you turn this attribute off, IBL switches to Finite mode. In Finite mode, IBL behaves as a finite sphere, where translation and uniform scaling are supported. Photon and light emission behave as point lights, not directional lights, so that IBL can be used for closed environments. To avoid artifacts, ensure that your IBL sphere encloses your entire scene.

Note:

In Finite mode, IBL may take more time to compute.
Toggling between infinite and finite may cause illumination to change (similar to toggling between point and spot lights).

Color Space

Allows you to specify the input color space used by the image. When color management is enabled, the color values are automatically transformed from this space to your working color space for rendering.

IBL nodes default to Raw, so no transform is applied on input. However, it is best to specify the exact color space used so that colors get properly converted to the rendering space if it is different from the file's space.

For more information about color management in general, see Color Management.

Ignore Color Space Input Rules

Prevents the Color Space that has been assigned from changing when you reapply the Input Color Space Rules. This is useful when you have manually changed the Color Space and do not want it to be changed if the rules get reapplied, for example, if you have a particular image file that uses a specific color space instead of the one set by the rules.

Light Emission

These are the attributes in the Light Emission section.

You can emit light from the IBL environment radially inward toward the origin (of world space). If light emission is turned on, the IBL node acts like true light sources in the scene. The IBL texture is mapped to a mental ray light shader just like a real light source would be.

Emit Light

Enable this option if you want to emit light from the infinitely distant IBL environment.

Quality

In Maya 2015, the Emit Light feature was improved to provide higher quality render results, and with a Quality control slider to adaptively control IBL lighting quality. This is the main control for adjusting IBL lighting quality when creating an IBL node, and provides a simplified user interface for IBL settings. You must enable the Emit Light option to take advantage of this feature improvement.

Access to legacy (pre-Maya 2015) controls are still available by enabling the User Legacy option and adjusting the controls via the settings in the Legacy section.

Use Legacy

Select this option to use the legacy (pre Maya 2015) quality controls.

Advanced

Resolution

Controls the resolution of the IBL acceleration data.

The environment is sampled and baked into data structures for accelerated lookup during rendering. Higher resolution provides better quality results but requires longer calculation time and more memory. Lower resolution provides less details such as soft shadows and highlights, even for strong hot spots in the environment.

Resolution Samples

Controls the quality of the IBL acceleration data.

Specifies the number of samples per measurement in the pre-process. If the Resolution is very low, this value can be used to increase the sampling quality of the environment. Higher values increase pre-processing time.

Color Gain

Scales the contribution of illumination from the IBL environment.

The illumination from the environment is multiplied by this factor; or, by this color (if individual RGB components are provided). The directly visible environment is not affected.

Legacy

Quality U, Quality V

The light shader sets up a “control texture” for light emission. Every pixel in that texture virtually represents a directional light. These values specify the control texture's resolution. Higher values offer more precision but are more processor intensive. Loaded IBL textures are downsampled to the filter resolution; procedural textures are sampled at this resolution in pixel units for optimum performance.

Samples

Sampling all “directional lights” represented by the control texture is often prohibitively expensive. Therefore the shader has a built-in importance mechanism that attempts to select the primary (key) lights.

The first Samples parameter specifies the number of important lights that must be sampled. The second parameter quasi-randomly selects a certain number of secondary (fill) lights.

Low samples

Low Samples specifies the number of light samples taken from IBL during final gathering. It defaults to 1/8th of the regular samples (that is, 5/2).

Vary Focus

Each “directional light” in the control texture sphere determines its direction. Turning on Vary Focus slightly offsets that direction (randomly) and thus improves quality.

Disable Backlighting

If lights on the backside of surfaces do not contribute to the surfaces' illumination (i.e., there is no translucency in the scene), you should turn this on. It optimizes sampling significantly.

Emit Diffuse, Emit Specular, Use Ray Trace Shadows, Shadow Color, Ray Depth Limit

These parameters are identical to attributes on Maya's standard lights.

Invert, Color Gain, Color Offset

These attributes are the same as those of Maya's texture node. They apply in similar ways to IBL.

For more information on texture nodes, see Overview of texture nodes.

Photon Emission

These are the attributes in the Photon Emission section.

Photons can be emitted from the IBL environment sphere. This requires Global Illumination and, or Caustic photons to be turned on in the Render Settings window. The emission direction is chosen randomly for individual photons. Similar to light emission, a photon picks up the color based on its emission direction from the IBL texture (file or procedural), possibly adjusted by color gain and offset. The results of this maps to a mental ray photon emission shader.

Emit Photons

Turn on, if you want to emit photons from the infinitely distant IBL environment.

Global Illumination

Determines how many global illumination photons are emitted.

Caustic Photons

Determines how many caustic photons are emitted.

Exponent

Determines the exponent used for photon emission.

Standard emission

If off, photons will be stored on first hit. This is useful if IBL is to be achieved using global illumination photons alone. In terms of a real-world environment you can think of this switch as photons from the Sun being scattered in the atmosphere before reaching any surface.

Turn this option on, if you are emitting caustic photons, or if you are emitting light in combination with photons.

Invert, Color Gain, Color Offset

These attributes are the same as those of Maya's texture node. They apply in similar ways to IBL.

For more information on texture nodes, see Overview of texture nodes.

Render Stats

Controls the IBL texture's visibility to certain ray types. This maps to a camera environment shader in mental ray. If all controls are deactivated, then no environment shader is processed. For classical image based lighting, the IBL texture must be visible to final gather rays. and Final Gathering must be on.

Primary Visibility: When on, the surface is visible in the view and renders.
Visible as Environment: When on, the surface is visible to environment rays (direct reflection of the environment). This attribute is off by default, unless you created the IBL node from the mental ray Render Settings window.
Visible in Secondary Reflections: When on, the surface is visible to secondary reflection rays. This attribute is off by default, unless you created the IBL node from the mental ray Render Settings window.
Visible In Refractions: When on, the surface refracts in transparent surfaces.
Visible In Final Gather: When on, the surface is visible to Final Gather rays and is used to illuminate the scene. When off, IBL does not affect final gathering. This attribute is off by default, unless you created the IBL node from the mental ray Render Settings window.