Example 1: The Subdivs parameter

Example 2: The Sample size parameter

Example 3: The Scale parameter

Example 4: The Retrace threshold parameter

Example 1: The Subdivs parameter

The Subdivs parameter controls the number of rays that are shot into the scene, and the "noise" quality of the light cache samples.

 

Here is a scene rendered with different settings for the Subdivs parameter, all other settings are the same.

 

Subdivs = 500
Subdivs = 1000
Subdivs = 2000

 

Example 2: The Sample size parameter

The Sample size parameter controls the size of the individual light cache samples. Smaller values produce a more detailed lighting solution, but are noisier and take more RAM. Larger values produce less detail, but take less RAM and may be faster to calculate.

 

Here is a scene rendered with different values for the Sample size parameter. All other values are the same.

 

Sample size = 0.01
Sample size = 0.02
Sample size = 0.04

 

Example 3: The Scale parameter

The Scale parameter determines whether the Sample size and Filter size parameters are in screen space, or world space.

 

In the table below, the Screen scale was used, and the scene was rendered with different image and world sizes. The Sample size was constant for all images - the default 0.02.

 

Scene scaled down to 50%
Normal scene
Scene scaled up to 200%
Resolution 250x300
Resolution 500x600
Resolution 1000x1200

 

In the table below, the World Scale mode was used. Again, the scene is rendered at three different resolutions and scales, but with the same light cache parameters. The sample size was set to be 1/5th of the sphere radius in the scene at normal scale.

 

Scene scaled down to 50%
Normal scene
Scene scaled up to 200%
Resolution 250x300
Resolution 500x600
Resolution 1000x1200

 

Example 4: The Retrace threshold parameter

The first set of images shows how the Retrace threshold parameter can be used to reduce light leaks due to the light cache interpolation. The scene is an interior scene with parts of the exterior visible. The bright light cache samples from the exterior blend with the darker samples from the interior causing light leaks when the irradiance map is calculated. The Retrace threshold option (with the default value of 1.0) successfully resolves the problem at the expense of slightly increased calculation time for the irradiance map.

 

Note: the model for this example is created by Urbanimmersive.

 

Without retracing, light cache samples from the bright exterior are mixed with the dark samples in the exterior causing light leaks. With light cache retracing enabled, the light leaks are successfully eliminated at the expense of slightly longer irradiance map calculation time.

 

The second scene in this example shows how the Retrace threshold option can be used to improve the appearance of glossy reflections and refraction with the Use light cache for glossy rays option. In this case, V-Ray dynamically decides whether to use the light cache or not, based on the glossiness of the surface and the distance from it.

 

Without retracing, the light cache samples are clearly visible in the glossy reflections and refractions. With light cache retracing enabled, V-Ray is able to dynamically decide whether to use the light cache or not, leading to a much better result.