Noise pattern of any camera through DaVinci

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sergisanchez

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Noise pattern of any camera through DaVinci

PostMon Oct 03, 2022 10:13 am

Hello all!

I stumbled across a tutorial explaining how, I believe using the layer mixer and/or the Splitter/Combiner node there was the possibility to isolate the noise pattern of your footage (in order to overlay it afterwards on denoised clips from the same camera).

Unfortunately I cannot recall where I saw / how to replicate that technique.

Any tips here on how do you get that?
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roger.magnusson

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Re: Noise pattern of any camera through DaVinci

PostMon Oct 03, 2022 10:41 am

There are several discussions about dark frame subtraction on the forum.
Try these threads:
https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=115570#p637406
https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=19422
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Jim Simon

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Re: Noise pattern of any camera through DaVinci

PostMon Oct 03, 2022 3:12 pm

1. Denoise

2. Analyze noise

3. Add noise to denoised clips


Seems...silly. Why not just skip it, leave the noise, if that's what you want?

What's the reasoning here?
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ZRGARDNE

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Re: Noise pattern of any camera through DaVinci

PostTue Oct 04, 2022 12:37 pm

Jim Simon wrote:1. Denoise

2. Analyze noise

3. Add noise to denoised clips


Seems...silly. Why not just skip it, leave the noise, if that's what you want?

What's the reasoning here?



I could see remove digital noise and add back filmic noise.
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Uli Plank

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Re: Noise pattern of any camera through DaVinci

PostTue Oct 04, 2022 1:24 pm

But that's no FPN then.
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Jim Simon

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Re: Noise pattern of any camera through DaVinci

PostTue Oct 04, 2022 1:58 pm

ZRGARDNE wrote:I could see remove digital noise and add back filmic noise.
Denoise I get. Film grain I get.

But in this case, the OP is wanting to remove the noise, then add the exact same noise back later.

That, I don't get.
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sergisanchez

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Re: Noise pattern of any camera through DaVinci

PostWed Oct 05, 2022 8:05 am

Jim Simon wrote:1. Denoise

2. Analyze noise

3. Add noise to denoised clips


Seems...silly. Why not just skip it, leave the noise, if that's what you want?

What's the reasoning here?


Hi Jim,
The reasoning behind is the following: imagine you have a 90min feature film to grade, shot on an Alexa Mini. The film has been shot at ISO 800, with a few shots being underexposed. You want to denoise the 5% of shots underexposed, and then applying the noise pattern of the "correctly exposed" shots on top, to give an uniform look.


I say "correctly" in brackets because we all understand that this is a subjective matter.
Makes sense now?

And thanks Roger for the FPN, it is a fascinating discussion but I believe there must be a easier way for this specific situation.
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Marc Wielage

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Re: Noise pattern of any camera through DaVinci

PostWed Oct 05, 2022 10:13 am

sergisanchez wrote:The reasoning behind is the following: imagine you have a 90min feature film to grade, shot on an Alexa Mini. The film has been shot at ISO 800, with a few shots being underexposed. You want to denoise the 5% of shots underexposed, and then applying the noise pattern of the "correctly exposed" shots on top, to give an uniform look.

I don't think this is practical, for a lot of reasons. You're assuming the noise pattern will be identical in dozens (or hundreds) of subsequent shots, but it doesn't work that way. It's a lot more random.

I think a much more practical solution is just determine a reasonable amount of overall TNR and SNR -- even using different Lum and Chroma values -- to the entire image, without the complications of a layer mixer. We tend to do scene by scene (overall, not necessarily shot by shot) in the NR pass, but do tests just to make sure there's no artifacts. In truth, a lot of times a little noise is not going to hurt anything. The one possible exception would be (for example) a very glossy makeup commercial or a high-key food commercial. For those, we'd probably scrub every frame and make sure it's 100% clean. But for a feature, particularly one shot underexposed... I don't think a completely clean look is the right idea.

Neat Video is another solution that has a lot more user-adjustable parameters, but note that it's very demanding in terms of hardware and costs roughly 50% as much as Resolve.
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Hendrik Proosa

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Re: Noise pattern of any camera through DaVinci

PostWed Oct 05, 2022 10:25 am

Subtract denoised image from original, this will give you noise (make sure negative values are kept). Add that noise over some other denoised plate. Done.

In practice it isn’t always so easy though, problem with simple methods is that denoisers almost always remove some of the actual detail and this will show up in noise element as ”ghost image”. If you then plus this on top of different plate you get this ghosting added too, which can be obvious and distracting. And also noise strength will be different because it depends on pixel luminance of original image, so on new plate there is a mismatch.

How this is approached in real vfx comp is that noise profile (channel values vs noise strength) is created from noise element, then noise is recreated using either statistical profile, normalizing noise element using said profile or patch scattering methods (using a clean section of noise element) and this new noise element is then scaled according to profile and plussed over denoised plate again.

If this subject is of interest, check out DasGrain which is now very widely used by compers because it is really very good at what it does: https://www.nukepedia.com/gizmos/other/dasgrain
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drknsss

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Re: Noise pattern of any camera through DaVinci

PostWed Oct 05, 2022 1:01 pm

I saw a few short films (shot on film and digital) in a theatre recently with a distinct noise pattern throughout , so I see how you could look at a cut of a film and want to match the noise in certain scenes and shots to the whole. it seems very subjective, especially to a producer or director sitting behind the editor in a suite looking at the cut and pointing this out. I will say the noise patterns and the difference between them from scene to scene are VERY apparent with shots that liast for 1 minute or more(like in many indie films) as opposed to quick cuts of 15-20 seconds . In the long scenes where there is one shot for a long time, the noise gets more prominent as the seconds tick by...
Last edited by drknsss on Wed Oct 05, 2022 7:06 pm, edited 1 time in total.
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Dermot Shane

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Re: Noise pattern of any camera through DaVinci

PostWed Oct 05, 2022 4:00 pm

DVO re-noise?
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Marc Wielage

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Re: Noise pattern of any camera through DaVinci

PostThu Oct 06, 2022 1:50 am

drknsss wrote:I saw a few short films (shot on film and digital) in a theatre recently with a distinct noise pattern throughout , so I see how you could look at a cut of a film and want to match the noise in certain scenes and shots to the whole. it seems very subjective, especially to a producer or director sitting behind the editor in a suite looking at the cut and pointing this out.

There is a philosophy -- one that won a Technical Oscar for inventor John Lowry -- where you remove all the noise from the image, then go back and composite back in a sampling of the noise so that it's precisely-controlled and consistent in every shot. This kind of "grain management" is typical for major film projects, particularly when they have to apply the same grain to all digital VFX shots for consistency.

I don't know if this is practical for most productions, but I think a combination of experience and good judgement can tell you when the noise has become a distracting problem, vs. when the noise is minor and can pretty much be ignored.
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Re: Noise pattern of any camera through DaVinci

PostThu Oct 06, 2022 2:26 am

Mostly I approach in this way:
Whatever is the noise of the principal camera correctly exposed, stay.
For underexposed ones, I ‘Denoise’ until the amount/look n feel, feels similar to the principal camera.

If you saw “the woman king” in the theater, (great movie BTW) that was done in that way, (plus add a film grain layer because client want it, same amount overall): in few shots/scenes the sun went out at the wrong moment and I had to hit it harder to match.

At the end of the day, remember that even in the theater you will pas in a compression scheme that will attach high frequencies (noise), plus the actual light path/lens/distance/focus/keystoning will butcher the image, so, don’t make it too hard on yourself.
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Jim Simon

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Re: Noise pattern of any camera through DaVinci

PostThu Oct 06, 2022 11:28 pm

sergisanchez wrote:Makes sense now?
More than before. Thanks.
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sergisanchez

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Re: Noise pattern of any camera through DaVinci

PostFri Oct 07, 2022 8:56 am

Thank you for all the comments on this.

I'm relieved to see that my initial approach "denoise them but just a bit" was not just the easy method, but actually makes sense to most of you.

Good to know
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