Denoiser clamps render

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Egert_Kanep
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Denoiser clamps render

Post by Egert_Kanep » Mon May 28, 2018 9:27 pm

It seems like denoiser clamps bright parts of my images, I rendered image in 16 bit and used mostly area lights. When I used HDR image, it was working fine. Also sometimes denoiser doesn't start so I have to re render my image again.
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denoiser_problem.PNG

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Dade
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Re: Denoiser clamps render

Post by Dade » Mon May 28, 2018 10:17 pm

Egert_Kanep wrote:
Mon May 28, 2018 9:27 pm
It seems like denoiser clamps bright parts of my images, I rendered image in 16 bit and used mostly area lights. When I used HDR image, it was working fine. Also sometimes denoiser doesn't start so I have to re render my image again.
What do you mean with "rendered image in 16 bit" ? How many samples per pixel did you use ?

I don't notice any evident clamping in the attached image :?:
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Sharlybg
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Re: Denoiser clamps render

Post by Sharlybg » Mon May 28, 2018 11:30 pm

I don't notice any evident clamping in the attached image
In the image at the right you can see bright light comming beneath.

Maybe it is caused by anti spike option in denoiser ?
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B.Y.O.B.
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Re: Denoiser clamps render

Post by B.Y.O.B. » Tue May 29, 2018 7:36 am

Egert_Kanep wrote:
Mon May 28, 2018 9:27 pm
Also sometimes denoiser doesn't start so I have to re render my image again.
I have looked into this problem and I think I fixed it.
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Egert_Kanep
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Re: Denoiser clamps render

Post by Egert_Kanep » Thu Jun 14, 2018 4:49 pm

Another example of denoiser calmping render. Denoiser doesn't leave any values over 1 and therefore all information in highlights is lost, even if the values don't go over 1, its still destroys that information. It seems like denoiser outputs 8 bit image, not 16 bit float. In attached example on upper row I gained down images to see how they respond. As seen, all highlight info on denoised image is lost and bright parts appear flat, whereas info on raw render is still there. Also sometimes these rgb squares appear on denoised render, but only when using region. Just a side question, why deos denoiser kill alpha, I know I can use original image alpha, but wouldn't it be cleaner if denoised image already had correct alpha?
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denoiser_clamp.png

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B.Y.O.B.
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Re: Denoiser clamps render

Post by B.Y.O.B. » Thu Jun 14, 2018 8:07 pm

I can reproduce this.
In my particular scene, the effect is very strong with the Tile Path CPU engine, and rather weak with Path CPU (see the images here for Path CPU results).

The scene is attached.
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smoke_backlit_denoiser_clamping_bug.bcf
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scrn_2018-06-14_21-59-56.png
Tile Path CPU
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