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Let's take a look at the how to use the RotoPaint node to do garbage mattes for green screens and blue screens. Let's go get a blue screen picture. Punch up our Read node. We'll go to the NUKE WORKSHOP > Lesson_02_ Media, there is a blue screen, so we'll bring that in, add our RotoPaint node, hook it to the Viewer. All right, as I said, there are two general approaches. Sometimes you want to flood-fill the outside of the plate with a solid blue so the keyer will pull the key of the solid blue. So here's how we'll do that.
Punch up our Bezier, click on the good part of the picture here. Return to close. All right, so we've filled it with white. So the first thing we want to do is go over to the Shape tab so we can invert it. Click invert. So now we've flood-filled the outside but not with the right color yet. We'd go back to the Common tab, punch up the Eyedropper and Shift+Command to select a region to match the blue. We now have a perfect blue out here that the keyer will happily pull a very nice key.
The second garbage matting scenario is you've already pulled the key with the keyer and you want clear it out of the alpha channel and the pre multiplied foreground control. Let's take a look at that workflow. We will borrow the same blue screen element. Clear our Property bin. Let's use a Primatte keyer. I know we haven't done Primatte yet but that's okay. And then we'll attach to our Viewer. All right, first thing we are going do in Primatte is we'll select our backing color and then we'll go clear our background noise, get a nice good clean matte here.
Then we'll clear the foreground noise, just a quick and dirty matte to illustrate the workflow. That's all we want to do. Okay, let's pretend that's good enough and now what we want to do is we want a garbage matte black every where outside of this on both the RGB and the alpha channels. All right, so we'd go below the Primatte node and we'll add a RotoPaint node, select our Bezier, click, click, click, click, and this time, I am going to click to close.
Okay, now again we've flood filled with white. Same drill as before. Go to the Shape tab and set it for Invert and now we've got white outside but we don't want white. We want black. So we'll go to the Common tab and we'll just set the color down to black. Note that the output of the RotoPaint is four channels, RGBA, so,I have flood filled black outside on both the RGB and the alpha channels and now we have a beautifully garbage matted key.
We'll turn the overlay back on, go back to the RGB. I have reset the Viewer to RGB and turned the Overlay back on so we can take a look at how we might garbage matte a Luma key. For that let's clear our Property bin, get the Read node, go to our week3 media, select the desert.cin picture. Okay we'll add a keyer to this. Let's go up here to the Key tab. Now we haven't-- again we haven't talked about the Keyer node, but that's okay because we are going to take a look at the Luma key.
Okay, the way the Luma key works is it puts a grayscale luminance image in the alpha channel and then you get to adjust it here to pull a key on the luminance. Let's say we wanted to isolate those clouds, for example. Well this is the common problem with the Luma key. It captures more than the item of interest. So we now have all these rocks in part of our Luma key, which we don't want. All right so we'll select the Luminance key, insert a RotoPaint node, punch up our Bezier, draw a shape around the stuff we want to make go away, click to close.
Now we've flood-filled it with white. So let's go look at the RGB channels, which is exactly what we told our shape to do. The RotoShape default is it is going to output it in RGBA. So first of all, we don't want it in RGB channel. So we'll set the output to Alpha. Go back and look at the alpha channel. We now filled it with white but we want to fill it black, no sweat. Go to the Common tab here and just dial the color down to black and there you have it.
So hopefully, these workflow examples will give you a good idea on how you actually use the RotoPaint node to create shapes for masking and keying and garbage matting. Now let's take a look at how to use the paint part of the RotoPaint node.
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