Noise threshold, no clue what's happening

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juangea
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Noise threshold, no clue what's happening

Post by juangea » Mon May 17, 2021 11:40 am

So I'm testing Noise Threshold on windows with 2.6 but I noticed something weird, or I don't understand how it works or something is off.

I did some tests with noise threshold in one scene and I saw on the terminal how the "ToDo Pixels" amount was descending, I had a Samples Amount limit of 1024.
The noise threshold was configured at a high value on purpose, I had it to 150, and both the warmup and the test step samples to 16, I played with different values and I noticed no difference.

Then I went and disabled the Samples halt condition and I configured the Noise Threshold to 255, warmup and test to 16.

The render stopped at 1285 samples, shouldn't the noise threshold at 255 give me a super noise image, but near to instantaneous?

I mean, it's the biggest possible threshold, but I don't get a stop until sample 1285, and the result was as expected for that amount of samples.

Any ideas?

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Dade
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Re: Noise threshold, no clue what's happening

Post by Dade » Mon May 17, 2021 12:04 pm

Are you using some kind of tile-like rendering with Sobol sampler ? Cache-friendly/Out-of-Memory settings ? Convergence threshold can work only with pure progressive rendering.

Can you post a test scene ?
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juangea
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Re: Noise threshold, no clue what's happening

Post by juangea » Mon May 17, 2021 12:14 pm

Ah, that's the thing then.

I'm using Photon GI Cache, Sobol and Cache Friendly, it's the scene I sent you for the linux bug, you already have it :).

I'll test without Cache Friendly and come back.

juangea
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Re: Noise threshold, no clue what's happening

Post by juangea » Mon May 17, 2021 1:35 pm

Mmmh, there was not difference, having it configured at 255 gave me 1760 samples, and it was slower than before (I assume that it was because I was using progressive and not Cache Friendly).

Shouldn't I get a super noisy image?

kintuX
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Re: Noise threshold, no clue what's happening

Post by kintuX » Mon May 17, 2021 11:53 pm

behavior also depends on Warmup & Test Step samples
I found 8 satisfactory

juangea
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Re: Noise threshold, no clue what's happening

Post by juangea » Tue May 18, 2021 7:30 am

Yes, I get that, but shouldn’t it stop the render after the first test with a threshold of 255?

Martini
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Re: Noise threshold, no clue what's happening

Post by Martini » Tue May 18, 2021 3:46 pm

juangea wrote:
Tue May 18, 2021 7:30 am
Yes, I get that, but shouldn’t it stop the render after the first test with a threshold of 255?
While the input is presented in levels (0-255) it is not based on output RGB colour space (0-255) but rather, the scaled raw float light intensity 0-Inf.

Imagine that 0.0-1.0 is the same as levels 0-255. If your light has realistic brightness (e.g. an HDR or Sun lamp) then it might be as high as 60000.0, which would be approximately 15,300,000 RGB levels. ;)

So if you have very bright lights and a lot of noise, it can take a long time to reduce noise down to the equivalent of even 255 above 0.
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juangea
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Re: Noise threshold, no clue what's happening

Post by juangea » Tue May 18, 2021 4:06 pm

Then Noise Threshold is nearly useless in those situations?

Martini
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Re: Noise threshold, no clue what's happening

Post by Martini » Tue May 18, 2021 5:02 pm

juangea wrote:
Tue May 18, 2021 4:06 pm
Then Noise Threshold is nearly useless in those situations?
You might need to adapt it to your scene and use a higher value.

:idea: If you watch the console output while it's rendering, it will tell you the current noise value. When you reach the desired (visual) noise level, that is your threshold.

Code: Select all

[LuxCore][188.640] Convergence test: ToDo Pixels = 1, Max. Error = 1.19853 [306.823/256]
E.g. if I was happy with the noise level when it printed this message, I would use the threshold 306.823

For reference, this is my scene with an HDR with halt condition at noise threshold 255:
noisy-255-threshold.png
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juangea
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Re: Noise threshold, no clue what's happening

Post by juangea » Tue May 18, 2021 5:09 pm

The thing is that in Blender we cannot put more than 255 I think.

@Theverat should know better I imagine.

P.S.: Yep, I just confirmed, in Blender the maximum value is 255, we cannot configure higher values.

P.S.2.: To Theverat (BYOB) I just changed the maximum limit of Noise Threshold from "max" to "soft_max" to allow freedom in maxmium written value, may be a thing to consider so the gates are open for custom values, what do you think?

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