Blackmagic Forum

Hi everyone,

I noticed something working with the Delta Keyer in Fusion. Under the matte tab, if I go to "replace mode" and select anything other than "source," I get a lot of extra noise. Presumably this is because Fusion is replacing the greenish bleed over my subject over the green screen.

I made a quick video to compare. The first half is replace mode set to "none," and the second half set to "source." I see more greenish colors in the second half, but it's also a lot less noisy.
https://drive.google.com/file/d/1zE9SXR8k_vu9dOO-0XtiBXNq3ymqc7GF/view?usp=sharing

Is this expected? I'm wondering if there is something I did wrong on my end. Perhaps I used bad lighting (still learning here). If I bought resolve studio, could I do a good job addressing that extra noise in the color page? Or is there something in the delta keyer controls that I am missing?

Thanks for your input!
-Matthew

It's a common problem with the Color Difference keying method. Keylight does the same thing. I frequently use just the matte from Delta, combining it with the plate in a MatteControl and using MatteControl's own superior spill suppression.

It comes from the max() comparison between channels. Where green is higher than a certain threshold, it gets replaced with the replace color. But noise in the image can push some pixels over the threshold while neighboring pixels keep their color. You can try playing with the Reference color to try to smooth it out, but MatteControl is usually faster and better at suppression.

Thanks. I haven't used MatteControl before. Do you just send the Delta matte to the MattControl Background input, and then mess with the spill controls?

I also noticed that I could pull out some extra green with the color page.

If you're going to use the RGB output from Delta, yes. What I generally do looks like this:

Code: Select all

{
   Tools = ordered() {
      PipeRouter5 = PipeRouter {
         ViewInfo = PipeRouterInfo { Pos = { 275, 16.5 } },
      },
      DeltaKeyer1 = DeltaKeyer {
         Inputs = {
            BackgroundRed = Input { Value = 0.0797009840607643, },
            BackgroundGreen = Input { Value = 0.0773529857397079, },
            BackgroundBlue = Input { Value = 0.570544302463531, },
            LowThreshold = Input { Value = 0.577, },
            HighThreshold = Input { Value = 0.881, },
            RestoreFringe = Input { Value = 0.00291, },
            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 }
                        }
                     }
                  }
               },
            },
            AlphaShadowsGain = Input { Value = 1.145, },
            Input = Input {
               SourceOp = "PipeRouter5",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 330, 49.5 } },
      },
      MatteControl1_2 = MatteControl {
         Inputs = {
            ApplyMaskInverted = Input { Value = 1, },
            MatteCombine = Input { Value = 4, },
            Filter = Input { Value = FuID { "Multi-box" }, },
            MatteBlur = Input { Value = 2.48, },
            Passes = Input { Value = 16, },
            LowMatteThreshold = Input { Value = 0.258, },
            High = Input { Value = 0.938, },
            ["Garbage.MaskNest"] = Input { Value = 1, },
            ["Garbage.MaskInverted"] = Input { Value = 1, },
            PostMultiplyImage = Input { Value = 1, },
            SpillSuppression = Input { Value = 1, },
            SpillMethod = Input { Value = 2, },
            Background = Input {
               SourceOp = "PipeRouter5",
               Source = "Output",
            },
            Foreground = Input {
               SourceOp = "DeltaKeyer1",
               Source = "Output",
            },
         },
         ViewInfo = OperatorInfo { Pos = { 550, 16.5 } },
      }
   }
}


The top part of the MatteControl works much like a ChannelBooleans—you can grab a new alpha from the green input. At the bottom, make sure Post Multiply Image is checked to knock out the screen.

This method ensures that I know at a glance exactly what's been done to my RGB. I don't have to open up Delta to check its settings because I know it's only providing a matte. That's a personal compositing philosophy of mine—every step should be a discrete node on the graph to make it as visually clear as possible what's happening.

Thanks for all that.. very helpful to us lurkers too

I have created a template with that combination. The Delta Keyer can do some amazing things, but I've always struggled with its despill options. I'd unfortunately overlooked MatteControl -- I guess I assumed it was mainly for tweaking alpha channels -- and that's a super combination!

(I'm practicing keying skills using some old DV footage: interlaced, 1440x1080 with non-square pixels. I was always disappointed with what I was able to do back in the day -- even using name-brand keyers. Not sure if it's Delta or if I've "grown" but now I can get results that aren't superb but they are actually surprising considering the limitations of the footage.)

Thanks for the tip!

The Matte Control is incredibly powerful and I use it for so many different tasks in Fusion, I hate going back to Nuke because it doesn't seem to have anything similar. Also I have noticed this type of Noise when my key is not as firm as it should be (Alpha less than 1).

Yeah, I used Nuke for a bit about 8 years ago. It was cool, and I'd never heard of Fusion. (I'd used Shake for a while before that, but Apple killed it off.) And it does strike me that in several ways, Fusion is better than Nuke, except that Nuke has better support for Hollywood-style pipelines while Fusion is not as flexible in that way.

(And Fusion's network rendering seems to be notorious.)

I was working through a Natron compositing tutorial where the instructor used the B channel to create a matte. I forget how he did it, but Fusion's Bitmap node seemed more flexible and straightforward and I ended up using Saturation rather than the B channel to make my matte. Then I noticed that I could use the "Luma Keyed", which is really a channel keyer and using Saturation did about the same thing but with a couple more parameters I could tweak, so I went with that.

I changed the Replace Mode to Hard Color and that seems to have fixed my noise issues with this particular clip; not sure if this will be the same with other keyed projects.