Noise after green screen removal

NOISE ALL OVER THE SCREEN WHEN I REMOVE GREEN SCREEN IN BOTH FUSION (DELTA KEY) AND EDIT (3D KEYER) in DAVINCI RESOLVE 17.2:

When I remove a green screen using either 3D Keyer, or Delta Keyer, there is terrible noise all overt the screen, not just in the area where the green screen covered. (The green screen did not cover all of the frame as I shot against a side wall which was not covered by the green screen). I have never seen that before and spent a whole night trying to find a solution, in vain. I shot with BM Ursa mini 4.6k, in 4KDCI, and the file was it's native DNG format. The lens was Samyang 35mm T1.5.

<snip>

This is a common side-effect of the noise reduction spill suppression method used in DeltaKeyer. The Foundry's Keylight has the same problem sometimes. What I prefer to do is set Delta to output only the matte. Then I combine that matte with the original RGB in a MatteControl and use MatteControl's far superior spill suppression to reduce the green.

Here's a quick example. Obviously I haven't used any actual footage here, so it's not a real key. The Background node is a stand-in for a greenscreen plate:

Code: Select all

{
   Tools = ordered() {
      DeltaKeyer1 = DeltaKeyer {
         Inputs = {
            ViewMode = Input { Value = FuID { "Matte" }, },
            TuningRanges = Input {
               Value = ColorCurves {
                  Curves = {
                     {
                        Points = {
                           { 0, 1 },
                           { 0.4, 0.2 },
                           { 0.6, 0 },
                           { 1, 0 }
                        }
                     },
                     {
                        Points = {
                           { 0, 0 },
                           { 0.4, 0 },
                           { 0.6, 0.2 },
                           { 1, 1 }
                        }
                     }
                  }
               },
            },
            Input = Input {
               SourceOp = "Background1",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 751.333, 38.8788 } },
      },
      Background1 = Background {
         Inputs = {
            Width = Input { Value = 1920, },
            Height = Input { Value = 1080, },
            ["Gamut.SLogVersion"] = Input { Value = FuID { "SLog2" }, },
         },
         ViewInfo = OperatorInfo { Pos = { 634.667, 85.5454 } },
      },
      MatteControl1 = MatteControl {
         CtrlWZoom = false,
         Inputs = {
            MatteCombine = Input { Value = 4, },
            Filter = Input { Value = FuID { "Fast Gaussian" }, },
            SpillColor = Input { Value = 1, },
            SpillSuppression = Input { Value = 0.874, },
            SpillMethod = Input { Value = 2, },
            Background = Input {
               SourceOp = "Background1",
               Source = "Output",
            },
            Foreground = Input {
               SourceOp = "DeltaKeyer1",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 854.667, 85.5454 } },
      }
   }
}


Keylight doesn’t do any noise reduction and I think neither does Deltakeyer, the problem stems from despilling combined with keying in the same operation. Solution is to separate the alpha process from despilling into different steps as Bryan explained.

Bah.. I said noise reduction and meant spill suppression. What I get for posting right before I go to bed!

Hi Bryan and Hendrix
Thanks for your responses. Is there a 'how to do' reference I can follow to do this? Or a plug in that would remove the dirt?

Thanks
Chuba

See up there where I posted some code? Select all of that and paste it into your node view. The tools will appear, and you'll see how it's set up. Again, I didn't use real footage; the Background is standing in for an actual greenscreen plate.

You definitely don't want to post-process to remove this apparent noise because it's not actually noise. It's a side-effect of the keyer's spill suppression feature. If you take Delta's spill suppression out of the mix, then the problem should go away.

Hi Bryan
I can't seem to find the 'Node View' where the code should be pasted. Where is it?

Hi Bryan
I can't seem to find the 'Node View' where the code should be pasted. Where is it?

It's just the area where you've been making your Fusion composition. Just copy Bryan's node code, go to Fusion, click on the background, hit Control-V for paste.

Bryan brother, I created an account to thank you for this!!!!

<snip>

This is a common side-effect of the noise reduction spill suppression method used in DeltaKeyer. The Foundry's Keylight has the same problem sometimes. What I prefer to do is set Delta to output only the matte. Then I combine that matte with the original RGB in a MatteControl and use MatteControl's far superior spill suppression to reduce the green.

Here's a quick example. Obviously I haven't used any actual footage here, so it's not a real key. The Background node is a stand-in for a greenscreen plate:

Code: Select all

{
   Tools = ordered() {
      DeltaKeyer1 = DeltaKeyer {
         Inputs = {
            ViewMode = Input { Value = FuID { "Matte" }, },
            TuningRanges = Input {
               Value = ColorCurves {
                  Curves = {
                     {
                        Points = {
                           { 0, 1 },
                           { 0.4, 0.2 },
                           { 0.6, 0 },
                           { 1, 0 }
                        }
                     },
                     {
                        Points = {
                           { 0, 0 },
                           { 0.4, 0 },
                           { 0.6, 0.2 },
                           { 1, 1 }
                        }
                     }
                  }
               },
            },
            Input = Input {
               SourceOp = "Background1",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 751.333, 38.8788 } },
      },
      Background1 = Background {
         Inputs = {
            Width = Input { Value = 1920, },
            Height = Input { Value = 1080, },
            ["Gamut.SLogVersion"] = Input { Value = FuID { "SLog2" }, },
         },
         ViewInfo = OperatorInfo { Pos = { 634.667, 85.5454 } },
      },
      MatteControl1 = MatteControl {
         CtrlWZoom = false,
         Inputs = {
            MatteCombine = Input { Value = 4, },
            Filter = Input { Value = FuID { "Fast Gaussian" }, },
            SpillColor = Input { Value = 1, },
            SpillSuppression = Input { Value = 0.874, },
            SpillMethod = Input { Value = 2, },
            Background = Input {
               SourceOp = "Background1",
               Source = "Output",
            },
            Foreground = Input {
               SourceOp = "DeltaKeyer1",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 854.667, 85.5454 } },
      }
   }
}


Alternatively, learn how to use a Clean Plate node, supposed to be piped in the pink input of the delta keyer. It may help you as well...

Could someone help a noob out please? I've tried pasting the code onto my project and replacing the background node with my green screen clip, but now I'm completely lost as to what I'm supposed to do. At first my MediaOut is identical to my MediaIn, although the green screen looks greyer. When I do the Delta Key, it seems to work alright in Fusion, but when I go back to the Edit page the clip has no transparency whatsoever as if I hadn't touched it (even though the MediaOut in Fusion shows the keying). In any case, in the MediaOut in Fusion the noise is still there.

I've been playing around for hours trying to fix the noise and the only thing I've found that sort of works is if I do the Delta Key and only work with the Pre-matte and leave the view mode on Pre-matte, then there's no noise whatsoever, I have no idea why. The only thing is the Pre-matte doesn't seem to have the flexibility to allow me to fine-tune (for example there are green edges and I can't manage to remove them on the Pre-matte). If someone has a solution it would be super appreciated!

It looks like a common problem when keying green screen. The "garbage" is often left behind and its not always visible until there is a lot of movement. To see it use gamma and gain sliders in alpha mode in the viewer and use something like mat threshold slider in delta keyer to clean up the mat. Here are some screenshots to illustrate the process.

green_screen_problem.jpg (931.52 KiB) Viewed 544 times

sshot-3781.jpg (225.14 KiB) Viewed 544 times

Hey

I would not suggest to play with the threshold here, though we all know it really works eventually... And while we're there, since you seem not to be comfortable with keying in any way (no problem, you'll have time to learn), tweaking the pre-matte is not likely to lead you to your goal.
So what, if I shouldn't touch'em, what must I do ?

You need to pull a good key. This supposed "noise" is likely to be semi-transparent pixels or despill artifacts, meaning you don't address the whole range of the green you're supposed to wipe out as you should.
So in a nutshell, either you use a CleanPlate node as well and go this way, or you may want to pull your key with two delta keyers (don't be afraid, it's a classic and not difficult), or...as our friend above suggested, you tweak the threshold anyway but you're then exposed to kill a part of the edges, hair, floating stuff etc of your object...
BTW, you'd better show a pic of your green clip, he was very nice to show you an example but you should show yours to help us help you

And in any case, in the first place don't touch anything else in the DK parameters : in the KEY tab, focus on the green selection, in the MATTE tab, at the Replace slider chose "source", prior to anything else
And to address the green spill bleeding on the edge of you object or charachter, DON'T go here to the gringe tab but put another node after the DK called MatteControl : this one has a better algo to treat the spill

So I'm ok to help as well, but hey, first show a screenshot, it's so easier then...