HDRI And GPU problems

[pixela]

Hello,
I am very new to gpu rendering.

I have a scene setup with HDRI. (few different hdri on different domelights. but only one domelight is on for each render setup.
When I render the scene with GPU, it renders super fast but the lighting is different from the CPU render.

Is this is a known issue? or am I doing something wrong?

[hermit.crab]

Best you send a simple scene where the issue is present to support@chaosgroup.com together with screenshots of the differences. Also, mention this thread in your e-mail along with your V-Ray, host platform, OS, GPU drivers versions and GPU model/s.

[pixela]

Hi there,
Here are 2 renders with the same lighting setup (Dome with HDR):
The left one is cpu render. The right one is gpu render.


Tried with a different HDR.
This time difference is huge.
Left one again cpu and the right one gpu.

[hermit.crab]

Thanks for the provided screenshots. I understand that there is a difference, however, it is not reproducible on a simple setup, therefore, it is necessary to investigate the scene itself so we can determine what causes the issue. Please send the required files and information to the upper mentioned e-mail so we can begin investigating.

[pixela]

Already sent yesterday.

[Muhammed_Hamed]

pixela This is expected to happen, simple HDRI lighting on GPU is a bit brighter than CPU
Displacement, bump mapping, SSS and many other things won't match between CPU and GPU
It is best to decide which engine you are going to use at the start of project, swapping between them is not an option as you will run into the differences I mentioned here and other limitations
Think of the GPU engine as a different renderer, it uses different code which is optimized for GPU hardware
I render most of my projects on GPU and my current hardware is picked for GPU rendering. It will not take long to transition to GPU rendering if you want to

[Muhammed_Hamed]

Your second test is not an expected behavior though, the difference shouldn't be that big
keep in mind that the GPU engine doesn't use portals, so you will need to use the adaptive domelight.
Maybe the support guys could tell what is going on in the second scene.

[pixela]

I got an email from Support group confirming the lighting difference issue when hdr used with render multiplier other than 1 and/or intensity set to grey.

[Morne]

I got an email from Support group confirming the lighting difference issue when hdr used with render multiplier other than 1 and/or intensity set to grey.

Do you mean the render multiplier in the VRayHDRIMap? So is it a bug and that multiplier is ignored in GPU?

[viktoria.dimitrova]

There seems to be a difference between CPU and GPU results of a VRayHDRI map with an RGB output set to "Intensity as grey" and color space set to "Inverse gamma" with values different than 1. The render multiplier, in this case, amplifies the difference.
I have logged the issue (Bug-tracker id: VMAX-9350) for our developers to investigate further.