Green Screen Tips & Tricks – Part 4: Masking

Sometimes, no matter what you try, you just can’t quite get a perfect key. Maybe you had a light stand or a boom end up in the shot? Maybe you have a really bad hot spot or dark shadow? Or maybe you just had to use that really cool sword, but it keeps reflecting the green of the screen? Whatever the case, you can’t get a good key without losing something. So what do you do?

This is where masking really comes in handy. In earlier versions of Adobe, you were limited to using a garbage matte if you were keying in Premiere, which tended to be a bit cumbersome. However, as of CC 2014, Premiere now has a built in mask tool with many of the effects – most notably Opacity and Ultra Key.

Using the Pen tool under Opacity you can click to add anchor points (click drag to make curves) and draw around the subject in your scene. Once you close the path, everything outside of the path is rendered transparent. This lets you easily remove background shadows, hot spots or physical objects you do not want to show in the final composite. Be sure to start your mask at the beginning of the clip, click the stop watch next to Mask Path to begin keyframing, then scrub through and adjust your anchor points to follow with the actors movements in the scene.

mask 1

Not only that, but when used in tandem with an inverted mask on the Ultra Key, you can select an area you DO NOT want to be affected by the Ultra Key, essentially protecting it from being affected. While this can be used on an actor in a scene, I do not recommend it as it will require extensive keyframing to make work. Also, bare in mind that the color correction tools in Ultra Key should not be used if the inverted mask is employed as it could affect the clip unevenly.

mask 2

While I recommend the use of the mask on the Opacity with near every scene you key, the additional use of the Ultra Key inverted mask is best saved for scenes with a non-moving, inanimate object. This makes for a good work around particularly in the event of a shot being used that employs an object that is similar in hue to the keyed color.

composite for masking

That about covers it for keying. Subscribe to the iNHale Film blog for more content involving filmmaking! In future installments I will go into creating backgrounds for green screen and compositing.

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