Join Steve Wright for an in-depth discussion in this video Pulling the key, part of Compositing a Sci-Fi Force Field in NUKE.
- Now that we have the background all figured out, it's time to pull our green screen key. So, let's scoot over here. Let's bring our viewer out here and our green screen over there. We'll hook the viewer up to the green screen and see what we got. So, our character has been filmed on a green screen with tracking markers. So, first thing I need to do is to get rid of these tracking markers, so that the keyer doesn't have to try to key on two different greens. So the way I'll do that, is I'll select by read node, come over to the keyer tab and get me a primatte keyer.
And I'll hook my viewer up to that. Now, I am not going to use the auto compute, because that'll try to do all the green for me automatically. I want to target just these tracking markers here. So, I'm going to do the Smart Select background myself. I'm going to come in here, Command, click, and drag on that, switch to the alpha channel. Okay. Now, I only need to worry about the tracking markers that are in the vicinity of my character. So, I'm gonna clean the background noise next, and select more of these tracking markers.
Let's get in nice and tight so I don't miss. I'll click and drag on this, and click and drag on there, click and drag on here, and maybe over there. How about up here? Okay. Over here, let's get these guys. And maybe over here. Make sure I don't leave any. Got to be careful not to click the regular green screen. I got to stay only on these tracking markers, or I'm going to make a problem for myself.
Okay, let's move him over to the beginning. Go back to the beginning of the frame, and make sure that I haven't got any markers that I need. Okay. Aha, these guys here. So, let me click and drag on them, make sure that they get put into my key. Okay, it's going to be like that. Next, I need to firm up the rest of the matte. And to do that, I am going to use the matte sponge.
And instead of making this solid, make that solid. Make this solid. I'm going to gama down my viewer a little bit, so I can see any holes I've got. I'll move them forward in time. Okay, and clear up this, that, and the other. Okay. All right, let's see how we're doing here. Okay, I'll move him to the end of the shot. That looks good. Okay, we got a little spot here we'd like to fix.
And maybe there. Got to make sure I don't hit my tracking markers, though. All right, that looks pretty good. All right, so I've got a black key for my tracking markers. Now the question is, "What am I going to do with that?" There's actually several different ways you could use this, but the way I'm going to do it is, interestingly enough... First of all, let's switch our viewer to RGB.
I'm going to use a grayed node here on my green screen, and then I'll hook the mask up to my primatte node. I'm going to hook my viewer up to the grayed node. And what I'm going to do, is I'm going to color correct out all those markers, to make them match the main background color. So, let's switch to the red channel here. And I'm going to go down here to the gain and unfold it. So, I need to match the red gain.
So, I'm going to gain down my red a little bit till the tracking markers disappear. Oh, that's going the wrong way because I need to invert my mask. So, if I invert the mask, there we go, now I'll be just affecting my markers. There we go. Okay, so I'm going to dial down the red and try to zero it out in the red channel. Okay? Then, we'll switch to the green channel. Zero that down close as I can.
Not perfect, but it's a big help. Switch to the blue channel and bring those down. All right. And then back to RGB. And so you can see that the markers have essential... Most of them have gone away. This sets things up for the real key. So with a grayed node selected, let's get a new primatte node. This time, we can use the auto compute, because we essentially have one uniform green screen backing color.
So, let's select Auto Compute, switch to the alpha channel, and we'll start cleaning the background noise up here. So, I'll need to do a Command or Control rectangle shift. So, to clean this up here. All right. We'll check back at the first frame, make sure we're not missing anything. Okay, here's a little stuff here we can get rid of. All right. Maybe a middle frame. Now clearly he's going off the top, so we're going to have to roto this.
So, we'll do that shortly. And I'll go to the last frame. Okay, so this is looking pretty good. Now, I need to get him nice and solid. Again, I'm gonna to gama down my viewer so I can see any holes in him. And we'll switch to the clean foreground noise. And with a Shift, Command, or Control, I'm going to sample big regions here and get him all cleaned up. Okay, and we'll check an earlier frame. Make sure I'm not missing anything, okay.
'Cause the lighting changes, or different parts of the costume are exposed, depending on what frame you're on. And I'll check later over here. Okay, well maybe we could fix this knee right there. Okay. All right, that's looking good. Now, I'll put my viewer gama back to normal. And we're all set with the main key. Now, we've got some garbage matting to do. We'll see that in the next movie.
- Building a doorway animation
- Pulling the key
- Making garbage mattes
- Compositing the character in the scene
- Creating the force field effect
- Setting the timing
- Creating and positioning emitters
- Adding interactive lighting
- Refining the final look