This page provides information on the Environment Importance Sampling rollouts in the V-Ray GI Render Settings.
Importance sampling is a rendering optimization that aims to reduce variance (noise) when sampling blurry effects (glossy reflections, GI, soft shadows, etc.) or calculating photon maps. This optimization can also be used on HDR environment images to greatly reduce the sampling noise on objects that are lit by the environment or have glossy reflections that see the environment.
In most situations it is better to have Environment Importance Sampling enabled. You might want to disable this option only when using a simple color for the environment.
The Photon Emission rollout in this section controls the quality of Global Photon Maps and Caustic Photon Maps.
||V-Ray GI render settings|| > Environment Importance Sampling rollout
||V-Ray GI render settings|| > Environment Importance Sampling - Photon Emission rollout
Enable EIS – When enabled, V-Ray will export a Dome Light with the environment texture applied, thus enabling importance sampling on the environment texture. If the environment textures for GI and reflections are different, V-Ray will use two separate dome lights.
Environment subdivs – Controls the number of subdivisions used. This value is used only when Use Local Subdivs is enabled in the DMC Sampler options. Higher values will reduce noise, but will take more time to render.
Photon subdivs – Determines the number of photons emitted by this light when calculating the Global Photon Map. A value of 1000 subdivs equals 1 million photons.
Diffuse multiplier – A strength multiplier for the diffuse photons.
Caustics subdivs – Determines the number of photons emitted by this light when calculating the Caustics Photon Map. A value of 1000 subdivs equals 1 million photons.
Caustics multiplier – A strength multiplier for the caustic photons.
Photon target radius – Defines a sphere around the center of the dome light toward which photons are fired. This radius should encompass all glass and metal surfaces that you want to create caustics.
Photon emit radius – Defines a sphere around the center of the dome light from which photons are fired. This radius should encompass all geometry in the scene.