VrayIlluminance shows wrong result if material is completely black

[Robert1977]

Dear all,

we are just making a test with the VrayIlluminance Render Element. Illuminance is the light that is emit from a light source before it is absorbed or bounced back by a material, while luminance is the light after it has been absorbed/reflected by a surface, so far my understanding.
When I have a material of rgb 0 0 0 in diffuse and reflection, the illuminance seems to be completely absorbed, while it remains constant at all material adjustments different from black. See attached picture. Is this maybe an error?

Best regards

Robert

[vlado]

It is a limitation currently; as you see when the material gets darker, V-Ray puts less and less samples on it (it becomes noisier). In the limit when the material is black, V-Ray does not evaluate the lighting on that material at all.

Out of curiosity, when would you need to use a perfectly black material, as it is not physically accurate in the first place?

Best regards,
Vlado

[Robert1977]

Dear Vlado,

you are completely right, we wouldn't use a completely black material. I was just curious why it is like that. And we also saw the less samples in darker materials. Its good to understand how the engine works with putting less samples in that area.
Beside of that, I am also curious how i can use vray for a really good approximation of illuminance and tell the customer that the materials vray uses are physically accurate by about 80-90% if correctly adjusted. Do you know if there is a difference in the materials simulation between lets say Integra Specter or Inspire and Vray? Specter uses materials which say they have an reflective amount of maybe 30% and works with spectral colors, while vray uses the rgb model in materials to represent diffuse and reflective amount. From my biasedpoint of view - because i like vray so much - i would say there is no big difference. What do you think?

Best regards

Robert

[Robert1977]

Dear Vlado,

is it possible somehow to show the Luminance with Vray as well? Right now we have Illuminance, but Luminance would be great to see the influence of the materials. I know this is possible with Max Scanline or Mental Ray, but I don't want to use them.

Best regards

Robert

[Svetlozar Draganov]

It is possible to measure the Luminance by using VrayLightMeter:
http://www.spot3d.com/vray/help/200R...lightmeter.htm

[vlado]

The light meter is also about illuminance unfortunately. However in 3ds Max Design, you can use the Lighting Analysis render element which supports luminance, I believe.

Best regards,
Vlado

[Robert1977]

Dear Vlado,

with Max standard renderer (or Mental Ray, I don't know anymore), one can show both luminance and illuminance in Rendering -> Environment -> Pseudo Color Exposure Control. There you can switch between both luminance and illuminance. But this is not supported by the vray renderer.
Also you have the render elements "Luminance HDR Data" and "Illuminance HDR Data", but I haven't tested them yet, and don't know if they work with Scanline or Mental Ray.

Best regards

Robert

[vlado]

with Max standard renderer (or Mental Ray, I don't know anymore), one can show both luminance and illuminance in Rendering -> Environment -> Pseudo Color Exposure Control. There you can switch between both luminance and illuminance. But this is not supported by the vray renderer.

No, it is not supported. That's why I suggested the Lighting analysis overlay which works fine.

Best regards,
Vlado

[Robert1977]

Hi Vlado,

and this lighting analysis overlay is part of Max 2012 design but not 2009?Ok, will have a look at it tomorrow. Thanks for this!

Robert