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:

 

  • Spherical Harmonics - this approach is based on rendering light information, already precomputed in *.vrsh file by spherical harmonics baking engine. This method is suitable for flight-through animations or animations with changing environment. It is applicable to open scenes only. For more information see Spherical Harmonics Baking Engine.

    Advantages: Disadvantages:

     

  • 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

    Global IlluminationOn - turn indirect illumination on and off.

     

    Reflective and Refractive Caustics

     

    GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics 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, because reflective GI caustics usually contribute little to the final illumination, while often they produce undesired subtle noise.

     

    Ambient Occlusion

     

    On - enables the ambient occlusion pass

     

    Multiplier - a multiplier for the effect of the ambient occlusion

     

    Radius - this parameters determines the amount of area (in scene units) where the ambient occlusion effect is produced.

     

    Subdivs - controls the number of samples that V-Ray takes to calculate the ambient occlusion effect. Lower values render faster but produce a more noisy result.

     

    Primary bounces

     

    Primary 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.

     

    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. 

     

    Spherical Harmonics - this chooses the spherical harmonics as the primary GI engine. See the Spherical Harmonics GI Engine section for more information. 

     

    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.

     

    Secondary bounces

     

    Secondary Engine - this list box specifies the method to be used for the secondary diffuse bounces.

     

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

     

    Photon map - selecting this option will cause V-Ray to use a photon map for secondary diffuse bounces.

     

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

     

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

     

    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.

     

    Ray Distance

     

    The options in this group allow you to limit the distance traveled by each GI ray in order to optimize and speed up the rendering.

     

    On - enables the Ray Distance limit.

     

    Ray Distance - specifies the maximum distance which each GI ray will travel.

    Notes