What is a “garbage matte”? According to the all-knowing Wikipedia:
A “garbage matte” is often hand-drawn, sometimes very quickly made, and can be used to exclude parts of an image that another process, such as bluescreen, would not remove. The name stems from the fact that the matte removes “garbage” from the procedurally produced image. This “garbage” might include a rig that is holding a model or the lighting grid above the top edge of the bluescreen. Garbage mattes can also be used to include parts of the image that might otherwise have been removed by the bluescreen, such as too much blue reflecting on a shiny model (“blue spill”).
In this case, we start out with this raw footage, designed to be a green screen shot:
It is filmed in front of a green background so we can apply the green screen effect to replace the background:
Notice that on the left edge, there’s a little bit of green that wasn’t removed very well. And then there’s that black thing on the lower righthand corner…. that would be my head (more about my head later… or not). Those are the two things that we do not want to see in the video.
So what do we do? Garbage matte comes to rescue!
With garbage matte, we can define an area that we want to keep in the final picture and leave out the rest. In Adobe Premiere Pro, this is done by first finding the garbage matte effect under Video Effects => Keying, and drag it into the Effect Controls Window:
And then in the Effects Controls Window, you can start changing the coordinates of each of the four corners that defines that garbage matte region:
And if you had “Garbage Matte” selected (highlighted), you can just drag the four corners to define the desired region. Now we see Bobby, who’s within the trapezoid-shape region we defined, and we no longer see the two things we were trying to remove!
Garbage mattes have other uses too. For example, in Episode 12: Daylight Saving, I used the trick to put Moostifer into a car. More about that later…
How to do a green screen effect: the theory
How to do a green screen effect: a case study
Episode 12: Daylight Saving