Refining the key
Video: Refining the keyI got a good basic key in the previous movie. The next thing I want to do is refine this key particularly in the context of the background. So in this case I'm going to turn my background movie back on and now the brightness of the background really shows up any edge issues I have for this video. In area like this person's collar where I have a bit of a dark edge I don't really like this is a case where I've reduced Clip White too low and I've extended out to the opaque area too far to pick up part of the background. So I'm going to hold down Command on Mac or Ctrl on Windows and slightly increase its value back towards its default to reduce some of the harshness of some of those edges.
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Explore how to use the motion tracker and stabilizer built into After Effects and shows how to handle a variety of shots. Author Chris Meyer leads a quick tour of the third-party software mocha and demonstrates the workflow for The Foundry's KEYLIGHT, both bundled with After Effects. The course also covers tracking a greenscreen shot with a handheld camera and replacing its background.
The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.
- Understanding motion stabilization and keying
- Performing a track
- Applying tracking to effects
- Keying with KEYLIGHT
- Replacing images
- Improving the composite
- Garbage masking
- Dealing with interlaced footage
Refining the key
I got a good basic key in the previous movie. The next thing I want to do is refine this key particularly in the context of the background. So in this case I'm going to turn my background movie back on and now the brightness of the background really shows up any edge issues I have for this video. In area like this person's collar where I have a bit of a dark edge I don't really like this is a case where I've reduced Clip White too low and I've extended out to the opaque area too far to pick up part of the background. So I'm going to hold down Command on Mac or Ctrl on Windows and slightly increase its value back towards its default to reduce some of the harshness of some of those edges.
So now I've reduced the sum of the harshness around the collar. The other parameter that's worth playing with is the Screen Softness. How feathered to soft the edges around this actor. In this case where his clothes I expect to have a fairly sharp edge around the actor, so a low value is a good idea. However, later in this shot when he is further away and a little bit of out of focus and particularly when he is moving very quickly these are cases where I want to soften the screen a little bit to get a little bit more of an anti-aliased edge around the action.
You'll see a little bit of it particularly in this area of the shot, let me get some more. It might be more obvious what's happening. There we can see the head is a little bit more against the bright plants in the background, I'll increase the softness a little bit and you'll see where I'm feathering that edge better and blending it in, I might indeed want to slightly shrink the screen to tighten it up as well like around there. And again these parameters can be key- framed, I can go ahead and key-frame to this area where there is a lot of action going on, but start much sharper when the actor's close and should have a sharp background.
And I'll play around the cropping to not expose areas that I want to see, just clean them up nicely like about that, here we go. The problem with shooting on a green screen stage is you're going to get some unusual lighting and particularly you might get some green spill of that background. Fortunately, Keylight has some very good color correction built in. The quickest instant gratification color correction is to use this Despill Bias color.
I'm going to select the Eyedropper for that and pick the color that's supposed to be an accurate skin tone such as around this area of his head. As soon as I do so, you'll see that both actors now have a much healthier pink skin tone rather than the slightly sickly green skin tone from the green spill, I'm going to undo. That was the uncorrected shot, Eyedropper and that's the corrected shot, better tone. In addition to using the Despill Bias color to Despill or remove color spill both from the background, I've also found that this so-called Replace Method is very useful in blending in my color corrections.
The default to soft color, which is pretty good. In this case if I am concerned about the shot being a bit on the dark side another option is to use Hard Color which gives me lighter tones in a way things were blending in. And speaking of which, you don't need to rely just on Keylight to do your color correction to blend your foreground into its new background. Go ahead and feel free to add additional color correction effects after Keylight to better match the foreground and background elements. This case something is simple as Color Correction Levels may help me clean up the basic brightness.
I can drag the Gamma Slider to the right to make them seem to be more in shadows or I can drag the Gamma Slider to the left to make it seem like there is more sunlight hitting them through these exposed windows. I'll pick her compromised so it looks more natural. In my case I may preferred being more in the shadows like that, and there is other color correction effects almost powerful of all courses, Synthetic Aperture's, Color Finesse, but you can even use very simple things like a little bit of Hue/Saturation, Color Balance (HLS). One of my new favorite plugins from After Effects CS5 and later Vibrance, because not only does that give me Saturation controls to increase saturation or decrease it in a shot, it gives me Vibrance which is a much more subtle effect to go ahead and maybe beef up my saturation a little bit to get them better skin tone against my very strongly colored background.
And time for the payoff, I'm going to RAM Preview, and this is now my stabilized shot with the green background keyed out placed over a new still image in the background. Keylight is particularly good at semitransparent areas such as the Motion Blur when these actors are struggling with each other. And you see this works out, pretty darn well. I have done a very quick application of Keylight here. Normally keying is something you will spend many, many minutes on refining and getting a good look, because if you don't have a good key it's going to immediately giveaway, you've got a background and foreground that weren't originally shot together.
Spend some time on getting a good key, go ahead and read the Keylight manual from the foundry and you'll end up with some pretty nice visual effect shots.
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