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The purpose of the preliminary composite is to hook up the master key to the green screen in the background to see how things look and determine where the master key needs improvement. So we'll zoom out a little bit, pick our story up here with the original green screen. We're going to start that separate branch over here. All of this was our keying down here. And over here we're going to start with spill suppression, so we'll go up to our Color tab and do a Shift+Click on HueCorrect, which is a popular spill-suppression tool in Nuke, and hook up our viewer, and switch the viewer back to RGB.
And we'll zoom out so we can see our spill suppression. So the first step in the spill suppression is we're going to sample our green screen color, so we'll do that with a Shift+Ctrl+Drag. The HueCorrect node shows us that this is the hue that's the green screen. I'm going to use three curves to do the spill suppression, because I like to spread it out amongst three different processes. If you do all the spill suppression with one process, it can show artifacts, but if you'll use three of them, you get little artifacts in different places, and nobody will see them.
So I'll select the saturation and the luminance and the green suppress curves, and I want to shift their control points right over to the hue that I was supposed to be using. Okay, so now I'll select the green suppress curve. I'll pull down on that to do some green suppression here. Then I'll take the saturation curve and pull down on that to desaturate the picture, okay. And I will go to the luminance curve and raise that up to put back some of the brightest that we lost with the green suppression.
All right, so let's zoom in and take a look over what we've got. I've still got a little bit of green around the edge, so I'm going to select my green suppression curve and shift it towards the red to kind of cut that down a little bit. And I'm seeing a little bit of a dark edge over here, so I'll select the luminance curve and move that into the reds to help eliminate the dark edge. And I will re-home the viewer, so we can take a look at how our spill suppression looks. The next operation will be color correction, so let's move things a little bit, get this over here, pull that over there.
Let's label this spill suppression. That way we'll always know what it's doing. All right, here is the key thing about color correction. It must always follow the spill suppression. I am going to select this node, go up to the Color curve, and select the ColorCorrect node. The reason it must always follow it: if you put color correction first, then you do the spill suppression; if you make any changes to the color correction, it'll totally mess up your spill suppression, and you always make changes to the color correction.
So, it's essential that you go spill suppression first, color correction last. Okay, we're ready to pull our pieces together. Here I have the alpha channel, here I have the spill-suppressed foreground, and over here I have the background. Ao we are ready to hook things up in a basic composite. So I've decided to use the AddMix node for our composite because it gives us much more control over the edges than any other process.
So I'll come up here to the Merge tab and select the AddMix node, hook the B side up to the background, hook the A side up to our unpremultiplied foreground, and hook the viewer up to the AddMix node, and we don't see anything. I'll clear this color sample box by doing a Command+Click. And here are those extra curves we get with the AddMix node. We don't have a composite because the AddMix node expects the alpha channel to be coming in here on the A side, but that's an easy fix.
So what I need to do is introduce our key behind our unpremultiplied color-corrected, spill- suppressed foreground, and it's not there. What we want is over here. So here is our key, so all I have to do is copy it over here using the Copy node. There it is. We'll hook that in here. Now if I look through the viewer, I have my foreground and my key all together as a four-channel image, and that goes into the A side of the AddMix node.
And now the AddMix node will do a very nice composite, and I can use the curves to adjust the edges. Another important point about the AddMix node--let me put that at the top of Property bin--is this premultiplied option right here. If you turn this on, you're saying that this is a premultiplied image. If you leave it off, you're saying it is not. Now our image is not premultiplied, so this is correct. However, if I would like to use a premultiplied image, I could select the Copy node, come up here to the Merges tab, and add a premultiplied node.
So now I have a 4-channel premultiplied image coming into the AddMix node. So if I hook that into the AddMix node and I zoom in close here, I have to tell the AddMix node that the A side is now premultiplied by clicking this on. And you can see that it makes a very big difference. Okay, you must always be sure to correctly set the premultiplied option, depending on the type of foreground you have.
Once you get the preliminary composite setup, the next step is to compare the composite with the original green screen. So I am going to hook up input 2 of the Viewer to the original green screen. You then toggle between the composited view and the original view looking to see what is amiss. As you can see, we've lost a lot of fine detail on these feathers. In a regular composite usually it will be the hair. So what we need to do is create a supplemental key that is specifically optimized for just this fine feather detail and then somehow merge it in with our master key.
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