Join Steve Wright for an in-depth discussion in this video Isolating the doors, part of Compositing a Sci-Fi Force Field in NUKE.
- To start off, we're going to prep the background plate by isolating the doors. We need to cut a hole here so that when the doors open we can see into the back room. So to do that, we'll add a roto node by typing "o" on the keyboard. And I'm going to switch to a fullscreen view so we get a better look at what's going on. Let's switch to the Cusped Bezier because that's going to draw nice, straight lines. And to see better into these dark areas I'm going to bring up my viewer gamma. All right, so we've got to be careful and choose where we're going to put this.
We're going to cut it just inside this edge here, all the way around. So, I'll start by placing my points quickly here, here, here and there. Somewhere off screen, over here. There and close, okay. I'll rehome the viewer. Okay, I need to go tighten these up. So we'll come back as soon as I've got that done. Okay, all done tightening up my splines. I'll reset the GUI back to the normal display.
And now to punch the hole in my doors I need to take my roto node. Look, I'll select my shape here. On the row tab, I'll set premultiply to RGB. And that punched a hole on the wrong side of the picture. So that punched out the hallway instead of the doors. So, to fix that, we'll click on the shape tab and click on invert. There we go, that's what I'm looking for. I want a nice, solid alpha out here in the hallway and a nice hole for the doors.
Now let's cut the two doors. To do that, let's clear this. Let's set this roto aside and we're going to add another roto node. I'm going to hook this up here so we see the original plate. I'm going to set a new roto node off to the side. And the key is that I have set my property panel... My project settings are set for this job, okay. So my roto node is going to be the right size. Let's skip all of that, we don't need to worry about that. So if your project settings are not the right size you better fix them right now.
Or you'll be in deep kimchi. Okay, here's my strategy. I'm going to cut a mask for just the left door. Then I'm going to use that mask, along with the one we created for the whole door, to create the right door. Instead of trying to draw two perfectly fitting masks I'll draw one and derive the other. That way they'll fit perfectly. All right, so we'll open up this roto node. Then, again, I'm going to use the Cusped Bezier for straight lines.
Let's tap the spacebar and fill the whole frame. So I'll start drawing here, here, here, here. Well outside the door, well outside the door, and close. It's this edge that's critical. So I'm going to take a moment to come in and tighten up this roto. Okay, I'm all done tightening up this roto. Let's go back to our normal GUI view. Now let's see how we're going to use these two masks. The left door mask and the doorway mask to create the two door masks.
Looking at this roto node here, first thing I need to do for this alpha channel is invert it. So we'll select that, go to color grab an invert node, set that over here. All right. Now, we look at that one and we look at this one and what I need, is I want the left door roto that is inside this doorway. So I'm going to move this guy down here. Notice it's not connected to anything. And I'm going to go get a channel merge node.
I'll hook the A side up to the invert, which is my doorway. The B side up to this roto. Now let's take a look at what we've got. But if we set the operation to in now I have the left door that is inside my doorway shape. To make the right door, we use the same technique. We get a channel merge node. Hook up the A side to the inverted doorway.
Hook up the B side to my right door roto. And this time, we'll set the channel merge node for out. There. I'll clear my property bin. So now I have a left door and a right door and I know that they'll match perfectly. To use those to isolate the actual doors I'm going to need to copy in the alpha channel.
So I'll type "k" on the keyboard and get a copy node. I'm going to hook it up to here because that's where my alpha channel is for the left door. Hook the B side up to the original plate. And then to the copy node we'll add a premult. So, we'll come over here, add a premult. Now let's take a look at what we've got. Boom. Left door with a nice alpha channel. All right, we'll do the same thing for the right door. I'll select this channel merge node. Type "k" to get a copy node.
Hook that up to the original picture. And I just copy this premult here, command or control c. Select, command or control v. And now, if we take a look at that one, I have a right door. Okay. So I'll hook the viewer up to one premult, the other premult. Toggle, toggle, toggle. I got my two doors with lovely alpha channels. Next up, we'll see how to animate the doors.
- 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