Temporal Noise Reduction : Ghost images from previous clip

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lucacasa

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Temporal Noise Reduction : Ghost images from previous clip

PostFri Jan 10, 2020 11:14 am

Hi everybody!
When using Temporal Noise reduction on a single clip (which has been cut through an edl or manually), there is a ghost image, coming from the previous clip on the timeline, which appears in the first frame of the clip where the noise reduction is applied. (same for the last frame)
No way to have a workaround?
Neat Video Noise Reduction doesn't have this issue even if it uses also Temporal noise reduction.
Maybe this could be fixed in a future update by BlackMagic?
Many thanks
Luca
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Jim Simon

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostFri Jan 10, 2020 6:31 pm

Never saw that behavior myself. How may frames you using? (I typically use 3.)
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Michael_Andreas

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostFri Jan 10, 2020 9:20 pm

Does the problematic clip have handles for the TNR algorithm to use?

There are also settings for Motion Estimation that you could play with. Or you could set some keyframes to remove TNR from the 1st and last frame, maybe hit those frames a bit harder with spatial NR.
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Igor Riđanović

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostFri Jan 10, 2020 11:30 pm

Although you have a cut in the timeline, I suspect the clip you're degraining has a scene change one frame before your first visible frame. That's where the ghost image is coming from.
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Jim Simon

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostSat Jan 11, 2020 4:23 pm

Good thought, Igor.
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Robert Arnold

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostMon Jan 13, 2020 6:25 am

I have experienced this many times with the scene-detect/EDL workflow. The workaround I've found is:

1. Option-drag a copy of the clip in question up to the next track on the timeline
2. Remove your grade from the copy
3. Create an edit on the second frame of the copy and copy that first frame back a frame (basically, duplicate the first frame)
4. Go to the Deliver page and export the copy (with duplicated first frame) in some high-quality codec
5. Edit the new clip back into your timeline (it now has a handle at the beginning)

I feel like Resolve should detect when the frame it's trying to use is from a different shot (in knows how to detect cuts, after all), but for now, this is what I do.
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Michael_Andreas

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostMon Jan 13, 2020 1:42 pm

Can you get them to send you the project with one-second handles on each clip? That should cover this issue with TNR, and allow applying transitions or slipping a cut a frame or two.
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lucacasa

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 5:04 pm

Hi everybody,
sorry I was absent for a while.
Indeed no in this case I cannot change the workflow of the production.
The only solution was to put keyframes at the beginning and at the end of each clip. But this is a lot of work as I usually have hundreds of clip to denoise...

Juts to be more clear about the issue if it was not clear for someone.
Take a movie that need to be color graded.
Make an export .mov and an edl.
Import a timeline in Resolve with the cuts from the edl.
Then apply the TNR. For ex with 3 nodes
You don't see the issue all the time, you can see the issue particularly when there is a big change in luma between two shots. Ex first shot clear second shot dark.

Another way to overcome the issue is to use Scene cut detection and then Add cuts to media pool. This will add in the bin all the cuts as separate clips.
(Unfortunately I cannot change anything in their workflow for this production)

By the way Neat Video use also Temporal Noise reduction but does not have this issue. So an upgrade from Blackmagic would be welcome.
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Jim Simon

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 6:33 pm

lucacasa wrote:I cannot change the workflow of the production.


Why not? The one you're using is...odd.
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Michael_Andreas

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 7:06 pm

In DaVinci Resolve, the decision to export clips with handles is just a checkbox. I imagine that the major NLEs have this capability. How is asking them to reexport but with handles this time a change to their workflow?
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lucacasa

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 7:20 pm

I cannot ask to change the workflow because they use it since years and they don't want to change for me just arrived...

There is no handles in this case. It's an AAF from Avid but taken from a single file.
It means they have a timeline on Avid with a single video cut in many parts. Don't ask me why.

But my point is that Resolve could change the way to evaluate the noise, taking into account that there is a cut on the timeline so it shoudn't go to look on a previous clip, this would be much easier...
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Gary Hango

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 7:33 pm

Are you using a timeline based TNR node or clip based nodes? Clip based should not see frames from adjacent clips. If timeline based node, that’s probably the problem.
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lucacasa

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 7:45 pm

It's not a timeline based node, it's a clip node.
IT see it as a unique file because if you look in the media pool it's a unique file but it is cut ine the timeline in many clips.
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waltervolpatto

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostWed Jan 22, 2020 8:48 pm

if I understood correctly your issue, this is a common issue for either shots that have a first frame of slate or for already cut reels of a feature for restoration that you cut with an edl. also for already conformed pieces that you cut with an edl.

even if you cut a shot, there is always a frame of hidden tail that is the outgoing shot (or the incoming) and the TNR will look into it and use it. being a completely different image, the TNR will do a garble of it.

The recommendation to BM was to introduce a checkbox where the TNR ONLY use the frames that are visible (in the cut) for computation. that was a couple of years back and few threads deep in the software suggestions.

there are very few workarounds unfortunately....
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lucacasa

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Re: Temporal Noise Reduction : Ghost images from previous cl

PostThu Jan 23, 2020 5:17 pm

The recommendation to BM was to introduce a checkbox where the TNR ONLY use the frames that are visible (in the cut) for computation. that was a couple of years back and few threads deep in the software suggestions.

Thanks for your message, I hadn't found previous threads about it.
It's a shame blackmagic didn't hear it. Moreover I believe a lot of people use it and never realize that there are ghost images. Quite often you don't see it in play unless you stop at that frame.

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