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Using garbage masks for keying

From: After Effects Apprentice 12: Tracking and Keying

Video: Using garbage masks for keying

When keying in green screen or blue screen footage, you don't have to or necessarily want to key the entire frame. When you're using a keying effect, your focus is creating a really good edge close to the actor you want to keep. The rest is extraneous junk that you can use a duller edge tool like a mask rather than a keying plug-in to get rid of. Now this image provided by Alex Lindsay and Pixel Corps shows a wide shot of a full set that has many things going on. We can see the back wall, we can see different lighting stands in the image.

Using garbage masks for keying

When keying in green screen or blue screen footage, you don't have to or necessarily want to key the entire frame. When you're using a keying effect, your focus is creating a really good edge close to the actor you want to keep. The rest is extraneous junk that you can use a duller edge tool like a mask rather than a keying plug-in to get rid of. Now this image provided by Alex Lindsay and Pixel Corps shows a wide shot of a full set that has many things going on. We can see the back wall, we can see different lighting stands in the image.

All we want to do is just key the area around this man. We won't key the rest of this. Therefore, we would create a mask around our action, excluding anything that we know we don't need, such as these two stands here, and then focus on getting a good key just around that individual. In addition to very obvious things, such as he stands this piece of cloth off to the side, etcetera, lighting will vary across a green screen stage. You can see here, where it's a little bit dark where the screen bends off from the walls to the floor.

There is no need to try to get a perfect key off in this area, when the actor, the foreground, is never going to go over here. Don't waste your time compromising a good key around the actor, just to make other parts of the image look good. Now this is a simple shot where the person is merely walking away from the camera, not doing any drastic movement, one simple rectangular mask can work for the length of the entire shot. But the shot we worked with earlier in this lesson, I will switch back to After Effects, we had much more of a challenge with people entering the screen, etcetera.

Now when we keyed this shot we did it in a very simple sloppy way. We applied Keylight to the entire shot, picked the color close to the original actor, looked at our Status and adjusted the Black Clip and the White Clip to go ahead and create a good key, and there is solidifying the body. But this is an example of where down in this corner, I will go ahead and move this shot over; I had to do some extra work just to get that corner to key out.

It would be much better if I masked it, particularly when the actor has moved away from that particular corner. Then I don't need to cut in nearly as much with a Clip Black parameter as I did before. So this shot would be an excellent candidate to do a garbage mask on. In this case the actors are moving, I will need to animate my mask. Since I have two actors, I might even animate two different masks and try to create one Mask Shape that works for them both. So in this case, I go to the Pen Tool, I probably would select RotoBezier because it is easier to create quick or getting masks with.

I'll select that tool and just start cutting out roughly around the actor or matte it, I am going to cut out the tracking dots as well, so I don't need to worry about keying their color correctly, either, there, there and close. If you are on my mask, the shortcut is just to press M, keyframe, the mask path then move later in time and keep updating the Mask Outline to track the actor. I'll press V to return to my Selection Tool, I could even double-click the entire Mask Shape, move it over, use the Free Transform to scale the mask to better fit where this actor is, pressing the Spacebar I am moving upward with Hand Tool, double-click for Free Transform, and go ahead and crop that in as well like that.

You don't need to edit every single mask point, sometimes it's easier to just alter the entire Mask Shape. I see I have a row keyframe here, I will delete that since all the information will be picked up in this keyframe. There's my animated mask following the actor in, cutting out a bit of the head there, I don't want to do that, so I'll edit my Mask Shape to make sure I don't lose part of the head right there. And you get the idea. I would create this Garbage Mask for the rest of the shot, watch for things like this shoulder here, move it across, move up a little bit, squish down this further away, and again, I could go ahead and edit individual mask points if I wanted to.

For example to make sure I was getting rid of these tracking dots where I could and then I'll create a second Mask Shape for the second actor, and add that in as part of the key. You will find quite often, particularly with visual effects working in After Effects, that putting in some extra time upfront, such as creating a Garbage Mask will save you a lot of time later for tasks such as keying. So it's worth learning these tricks were you can make your life easier down the road, rather than struggling with your tools.

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Image for After Effects Apprentice 12: Tracking and Keying
After Effects Apprentice 12: Tracking and Keying

39 video lessons · 14155 viewers

Chris Meyer and Trish Meyer
Author

 
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  1. 9m 2s
    1. Welcome
      2m 38s
    2. The Tracker panel
      4m 24s
    3. Using the exercise files
      2m 0s
  2. 13m 25s
    1. Warp Stabilizer basics
      5m 59s
    2. Warp Stabilizer advanced parameters
      7m 26s
  3. 30m 6s
    1. Setting up a stabilization
      2m 57s
    2. Track points explained
      5m 48s
    3. Performing a track
      5m 11s
    4. Applying a stabilization
      2m 42s
    5. Cleaning up the results of a stabilization
      3m 0s
    6. Performing a motion track
      5m 57s
    7. Applying the results
      4m 31s
  4. 13m 48s
    1. The Radio Waves effect
      4m 16s
    2. Tracking the mountain
      5m 31s
    3. Compositing the effect
      4m 1s
  5. 24m 28s
    1. Perspective tracking overview
      2m 40s
    2. Tracking to a corner pin
      7m 1s
    3. Improving the composite
      5m 39s
    4. Tracking with mocha-AE
      9m 8s
  6. 31m 49s
    1. Tracking in 3D (new in CS6)
      4m 31s
    2. Creating 3D objects (new in CS6)
      5m 12s
    3. Hanging a poster (new in CS6)
      8m 8s
    4. Adding text (new in CS6)
      5m 33s
    5. Using shadow catchers (new in CS6)
      8m 25s
  7. 16m 46s
    1. Tracking dots
      5m 43s
    2. Dealing with obscuration
      5m 12s
    3. Cleaning up the stabilization
      5m 51s
  8. 12m 40s
    1. Basic keying
      7m 20s
    2. Refining the key
      5m 20s
  9. 13m 32s
    1. Quizzler challenges
      3m 35s
    2. Quizzler #1 solution: Stabilization plus masking
      2m 58s
    3. Quizzler #2 solution: Stabilization plus tracking
      2m 50s
    4. Quizzler #3 solution: Copying a camera's motion
      4m 9s
  10. 12m 28s
    1. Tracking for multiple effect points
      4m 44s
    2. Converting to ray-traced 3D (new in CS6)
      7m 44s
  11. 23m 59s
    1. Legacy tracker advice
      8m 14s
    2. Tracking interlaced sources
      5m 59s
    3. Using garbage masks for keying
      4m 51s
    4. Using the Rolling Shutter Repair feature (new in CS6)
      4m 55s

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