Light Tracing Too 'Powerful'

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Beinsezii
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Joined: Mon Oct 28, 2019 7:07 pm

Light Tracing Too 'Powerful'

Post by Beinsezii » Mon Oct 28, 2019 7:37 pm

When using the 'Add Light Tracing' setting in the path renderer, the generated effects eventually become way too bright and sometimes blow out given enough samples. Best explained with photos, so here they are:
toobright.png
Result of about 2500 samples. Way too bright.
explodes.png
Certain settings cause it to explode. IDK why.
normal.png
Result of about 1000 samples. What you'd expect.
LuxBidir_30m_d.png
Bidir HQ reference. Closest thing to ground truth. 30 minutes @4k + OIDN
And the blend file, which somehow became 18mb and is too big to attach.
Render and wait till about 1700 samples and it'll start getting brighter till ~ 2400 samples.

The issue persists in CPU if you run enough samples into it. Setting the light/camera ray ratio to something really high like 95% will cause it to embrighten or explode very fast.
Issue is not present on Bidir, at least not that I've been able to find.

I'm here instead of Github for now because I know basically nothing about 3d software outside of my playing around with shaders for fun, so it could be user error. Issue always happens at the exact same sample in the render, so I doubt its cosmic rays.
My hypothesis is eventually the large values of caustic light cause some sort of overflow in the normalization/tonemapping area.


Off-topic: any good ideas to simulate the discoloration in diffraction with cycles? The linked blend file also has my current experiment with 3 separate glass shaders for RGB at slightly different IOR's when using the cycles/eevee renderers.

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Dade
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Joined: Mon Dec 04, 2017 8:36 pm
Location: Italy

Re: Light Tracing Too 'Powerful'

Post by Dade » Fri Nov 01, 2019 1:59 pm

I have tried your test scene up to 5000 samples but I can not reproduce your problem:

5000.jpg

What version are you using ? I have fixed a problem in the past that could explain what you are observing, can you try if it happens with a daily build too: viewtopic.php?f=9&t=736
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Beinsezii
Posts: 2
Joined: Mon Oct 28, 2019 7:07 pm

Re: Light Tracing Too 'Powerful'

Post by Beinsezii » Tue Nov 05, 2019 1:57 am

You're 100% correct. Switching from latest stable (2.2) to latest alpha (2.3) fixed the value bug and color accuracy is significantly closer to bidir.
I had searched through the github closed issues and couldn't find anything directly related, so I didn't even think to try the new dev build.

Thank you for your time and help.

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