in Demo Lesson by Ciro Sannino

The splotches’ secret in V-Ray

This brief lesson is to clarify part of STEP-4 (Final Settings) and these topics
could be part of final exam to take the certification.

Have you ever got a render full of splotches with V-Ray?

Splotches are the classical disturb for approximated calculations (GI with irradiance map), and grainess is the classical disturb for direct calculations (v-ray lights, glossy etc..)

So if you get splotches you already know: let’s check what’s wrong with GI! (GI = Global Illumination) – Even if Irradiance maps is set to HIGH, look how many splotches I got with this scene:

This effect is reduced if I render with my final settings. In particular, reducing the Noise Threshold (in SETTINGS) from 0,01 to 0,005 this is what I get:

The problem is reduced but not at all! Secret is coming!! :-)
Just go to Irradiance map and increase:

Hsph Subdivs = from 50 to 100
Interpolations sample = from 20 to 50

Basically we have to see to V-Ray: produce more rays to spread into the scene. In many cases of splotches this trick helps in getting a more uniform GI:

And here we are, this is the final result:

Please check my scene with V-Ray final settings to get a clean result:

Download here this scene-sample

I hope this could help you in many situations!
Ciro Sannino
V-Ray Licensed Instructor

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Parameters Descriptions

To know more about these 2 important parameters, here is the official description from Chaosgroup:

Hemispheric subdivs (HSph. subdivs) :
this controls the quality of individual GI samples. Smaller values make things faster, but may produce blotchy result. Higher values produce smoother images. This is similar to theSubdivs parameter for direct computation. Note that this is not the actual number of rays that will be traced. The actual number of rays is proportional to the square of this value and also depends on the settings in the DMC sampler rollout. (for these reason when I reduced Noise Threshold from 0,01 to 0,005 this reduced the splotches!)

Interpolation samples :
this is the number of GI samples that will be used to interpolate the indirect illumination at a given point. Larger values tend to blur the detail in GI although the result will be smoother. Smaller values produce results with more detail, but may produce blotchiness if low Hemispheric subdivs are used.