Unnatural GI bleed in advance

[thanulee]

Hi, i get this weird thing with gi bleed in vray advanced. Why is that? Using IM+LC. Swapped to active shade RT and all is good. Thoughts? thanks

[thanulee]

Anyone? I dont wanna use override its weird

[savage309]

To be honest I have not idea what I am looking at.

Best,
Blago.

[thanulee]

Haha, well i have a yellow wall and on advanced is orange and wrong. In RT gpu is correct. It looks like the gi is bleeding all over the place. The proper wall color is on the 2nd image.
I deleted the scene so just make a box with an opening, add a vray sun, use similar yellow to what i have and press render in vray advance. Then try this in vray gpu. Vray advance is wrong.

[savage309]

As simple as the scene is, I would advice mailing it to support@chaosgroup.com for investigation

Best,
Blago.

[thanulee]

I will, im just reposting here with more details in case someone can help. Swapping between gpu and cpu i get other results (Gpu is correct).

scene file : https://www.dropbox.com/s/nl9d1iuvep...issue.max?dl=0

[Svetlozar Draganov]

I managed to replicate the issue, thankfully to the attached scene.
There is something suspicious with the VRay Exposure Control here. First its the feature that causes the discrepancy between ADV and RT, it is not supported on RT.
Second it shifts the final GI colors way too much, not sure if this is a bug or expected behavior yet. Will continue looking into it.

As for now you may disable VRay Exposure Control or replace it with Physical Camera Exposure Control which gives a more accurate results in this case.

[thanulee]

Thanks a lot.
U mean camera EV parameter instead? I ll give it a shot.

[Svetlozar Draganov]

Actually it is not from VRay Exposure Control, Physical Camera Exposure Control produce the same result when using the same values for Shutter Speed, F-number, ISO and White Balance.

[Svetlozar Draganov]

Try to increase the ISO parameter to something like 1000 and you'll get much closer color bleeding:

[thanulee]

Thanks. Still the bleed is really strong on the white. and in the corners. With BF is it any different? It should work with shutter and F proper though, right? I do not use iso for exposing images. I need specific values in my F and shutter in order to replicate mblur and actual dof of the real lens..

[Svetlozar Draganov]

BF won't be much different that IM in terms of bleeding. You may try to decrease the Saturation parameter from the GI settings, it will help to reduce the bleeding.
Please note that this is a closeup scene that is lit entirely with GI, its normal to have such amount of bleeding over the white floor and the corners.
Simple overriding of the GI material would be of extreme help here otherwise you have to battle with a lot of parameters and the final result won't be as good as the one with GI override.

[thanulee]

If i remember correctly the scene scale is normal and not small. I tried override ya, but its kinda unnatural. I think this should work 100% like gpu out of the box and not needing bias tweaks in the gi. I ll try in my full item scene, and if problem persists i ll let u know. thanks

[thanulee]

Any news on the subject? Will this be fixed? thanks

[vlado]

Part of the difference is because of the VRayExposureControl - we need to look into that.

The other reason for the difference is that the ActiveShade renderer performs only a few light bounces for performance reasons. The regular renderer uses the light cache to approximate hundreds of light bounces. The red component of your material is too bright (unrealistically bright, in fact) and so the red color bleeding is reduced only very slowly for each bounce, which is why the regular V-Ray produces such a different result.

If you switch the regular V-Ray to use "brute force" for the secondary GI engine, you will get a similar result as in ActiveShade. Alternatively, you can increase the number of GI bounces for ActiveShade to bring it closer to the regular V-Ray.

It might also make sense to use more realistic color values for your materials.

Best regards,
Vlado