Blue or Green Screens in the FxTree Keyer

How can you use the Softimage Fx Tree keyer to pull a blue- or green-screen in two clicks?

It’s very simple (and this applies to other applications as well).

The first thing to remember is that while running the keyer in HSV or RGB mode sounds like a good idea, it really isn’t.

Blue and Screen screen exist because they’re easy to key as a result of the keyable color being contained almost entierly in one channel.

So the first thing to do is changing the Keyer’s mode to Color Difference mode. Then, simply click the BG button and rectangle-select a green-colored rectangle on the image. You’re done.

The color difference keyer, just like the one in AfterEffects, compares one channel (red, green or blue) with the two others to create a matte.

“RGB” mode is the worse keying mode in practice and should never be used because it isn’t really what you have in mind, so at least stay with HSV mode if Color Difference does not work for you.

Jargon-Busting the Keyer

FG: Foreground image. This is the meteorologist or news anchor person. It is an image with a subject, and a green or blue area to key.

BG: The Background image, what will go behind the meteorologist. It has no green or blue screen area.

When you click BG, you’re picking the area where the background will go

When you click FG, you’re picking the area where the foreground is, to extend the tolerance

FG Pull: an optional secondary matte used to help pull the Foreground away from the green, for example to fix spill over hair. It helps fixing the foreground getting eroded by the green. Another practical example : you might get 95% of the way with the main matte in Color Difference mode, but need to remove some more green by combining that with a luminance matte. The FG pull matte combines with the ‘main’ matte, according to the mode in Matte Correct->FG Pull Matte Usage.


This page was last modified 03:57, 15 Dec 2010.
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