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Big difference in GI from overexposed surfaces in GPU vs CPU Arnold

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Message 1 of 5
Andrei_Goaga
1110 Views, 4 Replies

Big difference in GI from overexposed surfaces in GPU vs CPU Arnold

Hello,

I've found this strange behavior in Arnold.

 

If anyone could help out, please read down below and check the attached picture.

I've set-up this simple scene in Maya Creative 2023, with MtoA 5.2.2.1  and Arnold 7.1.4.1

I noticed that the reflections and the GI contribution from the blue wall that is hit by a direct sun light differ when using GPU vs CPU if the patch of light on the wall becomes overexposed. 

 

I've tried with higher Ray Depth samples for Diffuse and Specular and that made no difference.

 

Is this a GPU limitation or a bug or am I missing a setting somewhere?

 

Thank you,

Andrei

4 REPLIES 4
Message 2 of 5
thiago.ize
in reply to: Andrei_Goaga

Try raising the options.indirect_sample_clamp.

Message 3 of 5
Andrei_Goaga
in reply to: thiago.ize

Thank you very much! See attached.

 

That was it. I managed to get them looking similar. Even tough the red car paint material behaves a bit differently. I think that the specular reflections are now more powerful in the GPU one. 

 

I have raised the clamping to 200 for the GPU (from 10 on the CPU) in order to achieve the same illumination on the floor.

 

But things are now much more similar! Thank you!

Message 4 of 5
thiago.ize
in reply to: Andrei_Goaga

Glad that helped. You can raise this setting on the CPU as well if you want them to match. Ideally both would be set to infinity and you should then get the same results. The reason this setting exists instead of always having it at infinity, is that it helps remove noise. So there's a tradeoff between noise and correctness.

Message 5 of 5
Andrei_Goaga
in reply to: thiago.ize

Yes. I will play around with it. I managed to get the same perceived noise with CPU vs GPU in almost the same time. I have a 13900K and a RTX 4090 and they seem similar in terms of rendering times vs noise from what I can tell.

 

Thanks,

 

Andrei

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