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Final Cut Pro 3.0 Quick Tip #5

Keying explained By Stephen Schleicher
When doing postproduction, it seems every producer/director wants to, or needs to, include a shot or two that was shot against a blue or green screen wall. Your job is to blend it in with the rest of shots. First thought might be to jump over to a great program like Adobe After Effects to pull off the composite, but Final Cut Pro 3, does a pretty good job if you stay right inside the application.

Take your keyed footage and place it in V2 in the Timeline. Double click the clip to load it into the Viewer window, and from the Effects>Video Filters>Key menu choose Blue and Green Screen. This is a very simple keyer in Final Cut Pro and will serve nicely for this discussion.

The View area allows you select which view in the Canvas window you will see while working on your matte. Often when pulling the matte, you will want to have the view set to Matte, this way you can see the actual Alpha channel as you work.

The key mode tells Final Cut Pro which color you will be keying out. If your foreground subject is against any other color but Blue or Green, you will need to use the Chroma Key filter instead.

The Color Level is your way of telling Final Cut Pro what range of blue or green it should look for to complete the key. The higher the number the more area it will select.

Color Tolerance takes the Color Level value and determines how true it must remain to that color. If you have a Color Level of 42 for example, and a Tolerance of 10, Final Cut Pro looks roughly 10 values on either side of the number to determine the range. I tend to keep the tolerance level low, simply because my backdrops are a pretty solid color to begin with. A higher value would be useful if you have a backdrop with lighting or unevenness problems in your paint job.

Edge Thin is a simple matte choker, which will contract the matte if the value is positive, and expand the matte if the value is negative.

Working closely with Edge Thin is Edge Feather, which creates a smooth gradient around the edge of the matte. This is especially useful for blending the foreground object with the background layer.

In addition to being able to control the matte, you also can correct spill with Final Cut Pros built in Spill Suppressor. Spill is the unwanted light that bounces off the backdrop and falls on your foreground subject, this is a dead giveaway that a key is being done. The Spill Suppressor is simply a desaturation tool that targets a particular hue (in this case your background color).

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