Vray Matte Properties - Matte for refl/refr

[analog_studio]

Hey All

Long time user of Vray (20years) first-time poster (i think)

I noticed this and can't help but think its rendering incorrectly. I have attached a 3DS Max 2018 file for download.

When using the option for Matte for refl/refr turned on in the Vray Properties and also using Spherical Panorama with the FOV overrides set to 360/180 the test object renders at different brightness values when the camera is facing the opposite way from it. My theory is that because it is set to spherical panorama there is some screen space "thing" happening which does not take account of the camera override.

The attached scene is super simple and clearly demonstrates the problem.


michael merron

www.analogstudio.co.uk + www.vrpm.co.uk

[Miro]

This is a bug and is reported in the bug tracker under VMAX-7690. We'll post here on any updates.

[analog_studio]

OK. Great to know. Thanks for looking into it.

I will eagerly await a patch.

[hermit.crab]

Thanks for the provided scene. The differences in rendering results with an active and disabled 'Matte for refl/refr' option are expected. The reason for this is the separate methods with which V-Ray determines the correct material color. With the parameter disabled, V-Ray generates the objects' GI based on their applied material. With the parameter activated, V-Ray tries to determine the material's color based on the secondary matte environment (if active, otherwise the regular background) and the scene's lighting and generates the GI on that basis.

[analog_studio]

Thank you for your explanation.
The attached scene has a black environment and no secondary matte environment.

I would assume that on each frame as the camera rotates the teapot would render consistently. However, it changes brightness values on each frame as it rotates. I don't understand how your explanation accounts for that.

thanks again

[hermit.crab]

The difference is evident regardless of the animation and camera mode. The scene's lighting (GI environment override) is taken into account for the shadow generation when the 'Matte for refl/refr' option is active. Simply put, the parameter affects the GI. Compare the Alpha and GI passes for further clarification.

[analog_studio]

Im sorry but I cant see why there would be such a change in brightness.

the attached image is simply rotating the camera 90 degrees and it renders completely differently

[hermit.crab]

Pardon, we were talking about different things. I understood what you meant. After a talk with our developers, it seems the usage of the GI in the 'Matte for refl/refr' calculation (as explained earlier) is view-dependent. In some cases (like in yours) the secondary matte environment will be used (even though disabled, black color is taken). This leads to the difference in lighting direction. To resolve it, activate the Secondary Matte Environment and set its color to the GI color.

[analog_studio]

BOOM!

thanks for sticking with me on that!