VRayFastSSS2 is slightly different between CPU and GPU

[flat]

In V-RayNext, the textured SSS of VRayFastSSS2 is slightly different between CPU and GPU
It is not seen in V-Ray 3.6.

Test scene attached

[Alex_M]

Well, the difference is really not that big to be honest. Just tweak the settings of the material a bit until you match it. You shouldn't be switching engines mid-project anyway. Once you start developing a scene, stick with the engine you began with to avoid these little inconsistencies. If you started with Adv/CPU, stick with Adv/CPU. Don't change it halfway into it.

[flat]

Sorry, your answer is not an answer.

Chaos should not make minor tweaks to the user.
Developers should be able to modify the program side.

the V-Ray GPU and the CPU should be freely switched between each other.

In addition, there is no problem with 3.6, and it is necessary to explain the reason why the problem comes up in V-Ray Next.

[matanov]

the V-Ray GPU and the CPU should be freely switched between each other.

No, they shouldn't. They are two separate engines. Minor or major differences are possible both between the engines and their major versions.

[flat]

I understand that the V-Ray GPU is a different engine.

However, as long as you sell it in the same V-Ray package, it is the developer 's efforts to make sure that there is no difference as much as possible.

I made a new confirmation scene. It might be a trivial difference. But for artists it is a big difference.
I confirmed, but neither Tex nor GI nor reflections are involved. There is a difference in SSS calculation of purely FastSSS2.

Probably it is V-Ray GPU specification. I will say nothing more.


gpucpu_sss2dif.zip

[Muhammed_Hamed]

it is the developer 's efforts to make sure that there is no difference as much as possible.

Vray Next GPU gives different results compared to CPU in normal mapping, displacement, SSS and many other things
They are not supposed to be 100% matching. The GPU architecture in Vray has been written from scratch to meet GPU rendering specs and Chaos Group did an amazing job in this.
So you cannot switch from GPU to CPU in the middle of your project. Before you start you should decide whether you will use Vray GPU or Vray CPU
There is no point of trying to match the results between CPU and GPU
I think it might not be possible in many cases because GPU rendering has its own characteristics and limitations.
Just think of them as different engines

[Muhammed_Hamed]

If you are comparing this to Cycles for example, expecting the GPU and CPU results to match, Cycles on CPU is just running the GPU code on CPU like what Vray does with Hybird rendering.
So if you render your scene using the C++/CPU even if you don't have a GPU in your system, the result will 100% match rendering on your GPUs
But like I said above, Vray CPU is something different.

[oglu]

im fine with slightly difference. but if its to extreme i would become suspicious.
for example if we dont see a differenve from one shot to an other im fine with that. so im fine with the example above.
but if in one shot we see the char with brown hair (GPU) and in the other with black hair (CPU) something isnt in line.

[Muhammed_Hamed]

oglu Yup
The extreme differences might be bugs or things that are not supported on GPU
Usually you will be able to tell if something is wrong/suspicious and report it to devs.