Join Steve Wright for an in-depth discussion in this video How to cut and paste keys together, part of VFX Keying: Master Course.
- [Narrator] In this chapter we focus on building the UberKey, by combining multiple keys into a single master key. Many of these techniques also apply to the other workflow, where the full RGBA output of the keyers are combined into the final shot. We'll see more about that workflow in a later chapter. In this video, we'll see best practices for how to cut and paste the good parts of multiple keys together into a single master key. So, here's our setup. We start with our green screen and of course, our obligatory Denoise.
And down here, I've got three keyers set up. Now, we'll start by pulling a key on the head. Again, we're only concerned with the alpha channel so far. So, here is my best key for the head. And over here, I use Primatte for my best key for the body. So, I've drawn a Roto, which isolates the body. And we use the Keymix node to combine my best head with my best body. Keep in mind, the Keymix node is doing an over. Specifically, it's doing A over B.
So, they layering order is important. So, I want my Primatte body to be isolated by the mask and put over the Keylight head. Another important point is to choose the seam location wisely. You want to choose a spot that won't be seen, and is easy to keyframe. Because you're going to have to move this around over the length of the shot. Another very important point is to apply a feather to the Roto mask, to blend the edge smoothly.
Here, we'll take a look at the mask. You can see, we have a nice 20 pixel feather. Here's where the feather is important. We'll go back to the Keymix node. If I turn the feather off, and I'll turn the overlays off to get the spline out of our face. You can see we have a bit of a notch, because the two keys, made by two different keyers, or even the same keyer with different settings. The edges may not exactly line up. We're a little bit better over on this side. But over here, we've got a little step. So, having that feather in there will help to blend the two regions.
I'll re-Home the viewer. Now, I didn't get such a good show in my head Key. The feathers on the boy's head. So, I've done a whole 'nother key over here that was optimized just for those feathers. And we've also drawn a shape here. Let me zoom out a bit, so that you can catch that. So, this shape is going to isolate the key for the feathers. And then we're going to bring that in here and add it to the main key.
So, here's my body plus head, with disappointing feathers. And here, I've added in my good feathers. Again, the layering order, A over B, is very important. Watch what happens if I mess it up. I'm going to reverse the input order. So, I'm not really putting my body and head over my new feathers. You see, I don't get my fix. So, you have to get the layering order correctly. Put it back the way it belongs. And I'll re-Home the viewer.
And turn off the overlays. There is my UberKey, combination of three separate keys, tastefully blended together with feathered Rotos. We've seen how to combine the best parts of multiple keys to create the UberKey. But that's often not enough. There can be holes, or missing bits like the feather that need some separate, additional keying. In the next video, we'll see how to mix keys that are not made by a keyer with those created with other keying techniques, to fix any remaining problems in the key.
Note: This course was created by Steve Wright, author of the seminal book, Digital Compositing for Film and Video. We are proud to host this course in our library.
- Creating an uber key
- Keying green-screen vs. blue-screen footage
- Preprocessing footage
- Building a clean plate
- Making luma keys
- Keying on hue and saturation
- Pasting keys together
- Grain management
- Saving time with garbage mattes
- Using spill suppression
- Improving edges
- Color correcting keys
- Sweetening the comp
- Alternative compositing workflows
- Fixing edge problems
- Using KEYLIGHT, Primatte, Ultimatte, and other tools
Skill Level Intermediate
Photorealistic Lighting with Maya and Nuke (2012)with Mark Lefitz2h 24m Intermediate
Compositing a Sci-Fi Force Field in NUKEwith Steve Wright2h 12m Intermediate
Compositing an Alien Portal in NUKEwith Steve Wright2h 20m Intermediate
1. Keying Workflows
2. Pre-Processing the Green Screen
3. Other Types of Keys
4. Building the Uber Key
5. Spill Suppression
6. Compositing Techniques
7. Color Correcting
How to match grade two clips4m 15s
8. Workflow Examples
9. Sweetening the Comp
10. Fixing Edge Problems
11. Special Keying Solutions
12. Appendix: Keyer Tutorials
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