Poor light bounce results with Irradiance Map

[Alex_M]

On a job I'm working on at the moment I noticed strange results when using IM for primary bounces. It looks like the light bounces just a few times so areas that are not directly lit by the lights look like they are rendered without GI. I made a quick test changing the IM engine with BF and the results are MUCH better. Please check the screenshot below. Why does this happen? Does IM cast less light bounces than BF? You can even notice that the super bright lampshade casts a very dark shadow on the wall as if there is no bright lamp there.

[vlado]

Which V-Ray version?

Best regards,
Vlado

[Alex_M]

Vray 3.20.03

Which V-Ray version?

Best regards,
Vlado

[vlado]

I know there was an issue with GI through irradiance map when there was a dome light with "affect alpha" disabled, but in that case the IM came out brighter, not the other way round.

Is is possible to get us a part of the scene to support@chaosgroup.com so that we can check what's wrong?

Best regards,
Vlado

[Alex_M]

Ok, I will send the scene as soon as time allows.

I know there was an issue with GI through irradiance map when there was a dome light with "affect alpha" disabled, but in that case the IM came out brighter, not the other way round.

Is is possible to get us a part of the scene to support@chaosgroup.com so that we can check what's wrong?

Best regards,
Vlado

[baumgore]

Getting different bright GI between IM and brute-force here. BR gets brighter by around 10-20%.
Indoor, no sun-/skylight or Dome light. Some lights, a lot of GI bounces. Secondary always flythrough-LC.
Primary Single-frame IM or Brute force.
Can't post scene, it's confidential. Vray 3.30.01 and max 2016.
Will try to reproduce in small scene, no time now.

[svetlozar.draganov]

Make sure that Store with Irradiance Map option is deactivated for all the lights in the scene.
Light with that option enabled will be calculated only when IM is being used, in most of the cases though the result should be brighter with IM and darker with other GI-engines.

If possible please substitute the confidential information in the scene with simple primitives and materials and send it for investigation.

[Alex_M]

I just sent part of the scene to the support email for testing (the download link will be active for 5 days).

Make sure that Store with Irradiance Map option is deactivated for all the lights in the scene.
Light with that option enabled will be calculated only when IM is being used, in most of the cases though the result should be brighter with IM and darker with other GI-engines.

If possible please substitute the confidential information in the scene with simple primitives and materials and send it for investigation.

[svetlozar.draganov]

The result with IM is incorrect since Min and Max rate parameter are not set properly, the Min value is supposed to be smaller than the Max value which is not the case in your scene.
A warning about that is printed in the log file:



As soon as these values are set correctly the illumination between both engines becomes identical.