General

Approaches to indirect illumination

Primary and secondary bounces

Parameters

Notes

 

General

Approaches to indirect illumination

V-Ray implements several approaches for computing indirect illumination with different trade-offs between quality and speed:

 

Which method to use? That depends on the task at hand. The Examples section can help you in choosing a suitable method for your scene.

Primary and secondary bounces

The indirect illumination controls in V-Ray are divided into two large sections: controls concerning primary diffuse bounces and controls concerning secondary diffuse bounces. A primary diffuse bounce occurs when a shaded point is directly visible by the camera, or through specular reflective or refractive surfaces. A secondary bounce occurs when a shaded point is used in GI calculations.

Parameters

[GI interface]On - turn indirect illumination on and off.

GI caustics

GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics section to control direct light caustics. Note that GI caustics are usually hard to sample and may introduce noise in the GI solution.

 

Refractive GI caustics - this allows indirect lighting to pass through transparent objects (glass etc). Note that this is not the same as Caustics, which represent direct light going through transparent objects. You need refractive GI caustics to get skylight through windows, for example.

 

Reflective GI caustics - this allows indirect light to be reflected from specular objects (mirrors etc). Note that this is not the same as Caustics, which represent direct light going through specular surfaces. This is off by default, becase reflective GI caustics usually contribute little to the final illumination, while often they produce undesired sublte noise.

Post-processing

These controls allow additional modification of the indirect illumination, before it is added to the final rendering. The default values ensure a physically accurate result; however the user may want to modify the way GI looks for artistic purposes.

 

Saturation - controls the saturation of the GI; a value of 0.0 means that all color will be removed from the GI solution and will be in shades of grey only. The default value of 1.0 means the GI solution remains unmodified. Values above 1.0 boost the colors in the GI solution.

 

Contrast - this parameter works together with Contrast base to boost the contrast of the GI solution. When Contrast is 0.0, the GI solution becomes completely uniform with the value defined by Contrast base. A value of 1.0 means the solution remains unmodified. Values higher that 1.0 boost the contrast.

 

Contrast base - this parameter determines the base for the contrast boost. It defines the GI values that remain unchanged during the contrast calculations. 

Ambient occlusion

These controls allow you to add an ambient occlusion term to the global illumination solution.

 

On - enable or disable ambient occlusion.

 

Amount - the amount of ambient occlusion. A value of 0.0 will produce no ambient occlusion.

 

Radius - ambient occlusion radius.

 

Subdivs - determines the number of samples used for calculating ambient occlusion. Lower values will render faster, but might introduce noise.

Primary diffuse bounces

Multiplier - this value determines how much primary diffuse bounces contribute to the final image illumination. Note that the default value of 1.0 produces a physically accurate image. Other values are possible, but not physically plausible.

 

Primary GI engine - the list box specifies the method to be used for primary diffuse bounces.

 

Irradiance map - selecting this will cause V-Ray to use an irradiance map for primary diffuse bounces. See the Irradiance map section for more information.

 

Global photon map - selecting this option will cause V-Ray to use a photon map for primary diffuse bounces. This mode is useful when setting up the parameters of the global photon map. Usually it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

 

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffuse bounces. See the brute force GI section for more information.

 

Light cache - this chooses the light cache as the primary GI engine. See the Light cache section for more information. 

Secondary diffuse bounces

Multiplier - this determines the effect of secondary diffuse bounces on the scene illumination. Values close to 1.0 may tend to wash out the scene, while values around 0.0 may produce a dark image. Note that the default value of 1.0 produces physically accurate results. While other values are possible, they are not physically plausible.

 

Secondary diffuse bounces method - this parameter determines how V-Ray will calculate secondary diffuse bounces.

 

None - no secondary bounces will be computed. Use this option to produce skylit images without indirect color bleeding.

 

Global photon map - selecting this option will cause V-Ray to use a photon map for primary diffuse bounces. This mode is useful when setting up the parameters of the global photon map. Usually it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

 

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffuse bounces. See the Brute force GI section for more information.

 

Light cache - this chooses the light cache as the primary GI engine. See the Light cache section for more information.

Notes