From the course: VFX Keying: Master Course

Compositing keyer outputs - Nuke Tutorial

From the course: VFX Keying: Master Course

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Compositing keyer outputs

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- [Steve] This chapter combines the topics we've covered so far, keying workflows, pre-processing the green screen, building the uber keys, spill suppression, and compositing techniques, into various example workflows for creating complete green screen composites. Refinement techniques like white wrap and edge treatments are covered later in subsequent chapters. Here we'll focus on how the big pieces go together. This first video is about the simplest workflow combining the keyed outputs of multiple keyers without making a separate uber key. So we are using the spill suppression that comes with the keyer. Let's take a look at the soft comp hard comp technique. First, we'll push in here, then you start with our green screen, where you do our obligatory denoise. And that goes to our Keylight keyer. The key issue here is we have pulled a soft comp. Let me show you the alpha channel. If I gamma down the viewer, you can see we do not have a solid core, because I've optimized the Keylight settings for the best possible edges. Didn't care about a solid core. Remember as you jack up that solid core, it tends to chew in on your edges. So we're gonna take advantage of that. Alright, so I lay that down on the background, but the problem is it's not solid, as you can see, I've turned on these little white lights and you can see we have transparencies all over the place. So with that as a background, we get a second keyer. Now by the way, the second keyer can be a different keyer, like here, I'm using Primatte, or it can the same, like another Keylight, but just dialed differently, to get a nice solid core. So this one focuses on the core without worrying too much about the edges. We then take this hard comp and composite it over the Keylight background. And we get the best of both worlds. So I can show you that here. If we zoom in on the Keylight composite, you can see I have lots of lovely hair detail here. With my Primatte, not so much. But when I put the Primatte over the Keylight, I get the best of both. Okay, let's take a look at another workflow. The slice and dice, as I call it, cause we're gonna slice and dice different bits and pieces and cut and paste them together. Again, starting with our green screen and our spill suppression, we pull two different keys here. Now one is best for the man and the other best for the woman. Or best for the hair and the other one best for the shirt, or whatever difference you'd like to make. What I'm gonna do is use a Roto to KeyMix the two together, so this Roto here, let me put my viewer on that, has a nice, soft edge for the transition, which is very important when we KeyMix them together. You want a nice transition between the two different ones. So over here is my Keylight, over there is my Primatte. Close that, switch back to RGB. So I now have a four channel, pre-multiplied image that's sliced and diced with the best pieces put together into one. I can then comp that over my background. Now by the way, I used a Roto here to make the key for the KeyMix. This could have been a luma key or a hue key, or any other kind of a key you wanted, to isolate the object in question. Doesn't have to be a Roto. Again, we gotta keep an eye on our spill suppression, because the spill suppression on this side is from Keylight and spill suppression on this side is from Primatte. If we have an easy key, this can be your fastest workflow. Just keep an eye on that spill suppression difference. Next, we'll take a look at a basic uber key workflow.

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