V-Ray for Rhino Manual - Rum

Primary Engine: Irradiance Map
It can only be used for primary bounces. Open file Cups-Irradiance Map.3dm and open the Irradiance Map
control panel under Options. There is a very important setting option here related to image quality: Min Rate
and Max Rate.
Default for Min Rate and Max Rate are -3 and 0. In this file they are currently -8 and -7. Render it and you will
get image as below. Notice that the calculation speed is very fast, but the shadow and illumination quality are
low. There are splotchiness and artifacts as well
Min Rate: the control of minimum sample for each pixel. 0 value means 1 pixel as 1 sample. Value of -1 means
2 pixels as 1 sample. Value of -2 means 4 pixels as 1 sample and so on. Smaller value means fewer amount of
samples been taking from the object, so the render qualities of shadow, reflection and refraction are not very
good. Opposite way will result in better quality but longer render time.
Max Rate: To control the maximum sample for each
pixel. 0= 1 pixel uses 1 sample. 1= 1 pixel uses 4
samples. 2= 1 pixel uses 8 samples and so on. Smaller
value means fewer total samples used to calculate the
light. Opposite will result in better quality but longer
render time.
Default setting of -3 and 0 represent four passes of render job. From -3, -2, -1 to
0. So you can see the Prepass 1 of 4 to Prepass 4 of 4 from the render process
dialog box.
According to definitions above for Min Rate and Max Rate, it doesn't mean that -8
and -5 setting will have the same result of -3 and 0, eventhough each has the same
Users can have a low set of values for Min and Max Rate to render faster previews while creating the lighting
and material setting in the scene. For example: -6 and -5 or -4 to -3. Although the quality will very not be
good it will be okay for previews. After all settings are correct, then render with higher value to get the best
final quality image.
Image on the left is showing Irradiance Map's last prepass for a Min/Max Rate of -3/0. The image on the right
is the final result.
V-Ray for Rhino 67