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Exterior PT+HDRI = lots of noise

General discussion on lighting, backgrounds, Global Illumination, rendering parameters and tonnemapping.

Exterior PT+HDRI = lots of noise

Post Sat Apr 02, 2016 10:27 pm

Hi guys,

I'm currently trying to catch up with Yafaray and I notice there have been lots of improvements on many fields. Trying to render an exterior scene using an HDRI background and path tracing I'm getting an interesting lighting and nice window reflections but there's a lot of noise, not only on glossy/specular materials but also on diffuse ones.
Here's the image:
Image

And the render settings:
Image

Any suggestions to reduce the noise?

Regards,
Alvaro F. Celis
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afecelis
 
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Re: Exterior PT+HDRI = lots of noise

Post Sun Apr 03, 2016 5:37 am

Hello,

Please try the "clamp samples" parameter to 1.5 or 2.0. It could somewhat reduce realism of the scene (do tests to make sure it's still ok for you) but should reduce the noise a bit.

I hope it helps. Best regards!
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David Bluecame
 
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Re: Exterior PT+HDRI = lots of noise

Post Sun Apr 03, 2016 4:25 pm

Thanks a lot David! :D
I just tried it and indeed it now renders cleaner:
Image

Though render time took a lot longer and it still has a considerable amount of noise, specially on that black slate material, which is diffuse. So the only solution would be to keep cranking up the "clamp samples"? What do you mean by "It could somewhat reduce realism of the scene"? Or better said, how does increasing the clamp samples affect the rendered image?

My only concern, besides render time, is the inability to use this for animation since fireflies will be noticeable changing from frame to frame.
Which other rendering method would be suitable for an exterior scene illuminated by an hdri background?

I'm going to try a sunlight now to see how it affects the render.

Thanks for your dedication and support. I'm glad you're keeping Yafa's development active.

regards,
Alvaro F. Celis
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afecelis
 
Posts: 384
Joined: Fri Aug 19, 2005 1:17 am
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Re: Exterior PT+HDRI = lots of noise

Post Sun Apr 03, 2016 5:14 pm

Hello,

Improving noise in HDRI illumination is still a pending matter, but I hope to do something about it in future versions of YafaRay-E.

For now, clamping is a possibility but as you said, for dark materials it's not too good.

The problem here is that, in the HDRI, the "sun" area is small and very bright. This causes random bright samples in the materials (fireflies). Clamping allows reducing the brightness of those "rogue" samples at the expense of having a non-physically correct render. Realism may or may not suffer with clamping, but not being physically correct will have some effect in the final result.

However if the reduction in noise is more important than the physical correctness, then this clamp parameter will help.

For dark areas, the clamping does not work as well, as it's a maximum "absolute" clamping so still the contrast between those clamped bright samples and the dark material will be visible.

In that case, perhaps it could help doing this:
* Reduce the clamp to 1.0 for example.
* Increase the AA threshold to, for example, 0.05
* Set a Dark areas noise detection factor around 0.900. This reduces automatically the set AA threshold in the darker areas (proportional to the darkness). This could help the AA noise reduction focusing more on the dark areas.

Until a better HDRI solution is developed, that is what I would try... I hope it helps.
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David Bluecame
 
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Re: Exterior PT+HDRI = lots of noise

Post Mon Apr 04, 2016 2:02 am

whoah! Thanks a lot for the detailed explanation! :D

I'll try those new settings as well and see how things go. I did find something interesting, I hadn't mentioned, to take into account.
For the IBL background I used an exr image. I decided to run a test with an hdr and guess what? No noise whatsoever! :shock: :shock: I also disabled "caustic photons" in the world's options, in case they could also generate fireflies.
Image
So now I'm also wondering if the way each different format casts light/shadows has an incidence in Yafaray's rendering methods. I assumed exr would be more "compatible" since it's an open format that blender reads and writes without issues, but who would've known...

I also ran a test with a sun light + sunsky2 background and it renders out clean, but now I don't like hard shadows that much, and the global illumination is not as nice.

anyway, it's been very productive going through all this tests with your guidance and I'm really impressed by how far yafaray's capabilities have gone.

regards,
Alvaro F. Celis
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afecelis
 
Posts: 384
Joined: Fri Aug 19, 2005 1:17 am
Location: Colombia


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