Adding Effects to a Chroma Key Foreground in Avid

Generating a chroma key with an effect on the foreground.

A reoccurring complaint about how effects work in the Avid Media Composer editing system, is that if you apply an effect to a key, you end up affecting the background as well as the foreground.

This week we'll discuss how to add an effect to the foreground only. For this example we'll add a Chrystal effect to the foreground of a chroma key.

Start out with three video tracks in your sequence. Place your background on V1 and your green screen shot on V3. Leave the V2 track empty for now.

Show Alpha selected in SpectraMatte.

Add the Avid SpectraMatte to key your foreground (V3) over the background on V1. In my case, I'll be keying my foreground over a shot of Dead Horse Point State Park in Moab. Once you've adjusted the chroma key to get the best separation possible, select the Show Alpha checkbox in the Matte Analysis effect parameter.

Copy the foreground, without the SpectraMatte effect onto V2,  this will be the fill for your matte on V3. OPTION-drag a Matte Key effect onto V3, this will nest the SpectraMatte inside the Matte Key.

The Avid timeline with the Avid SpectraMatte nested in a Matte Key.

Another complaint about the Avid editing system is how it treats alpha channels. Avid treats alpha mattes the opposite of everyone else. Instead of the white being used as the key for the foreground and black used for the background, Avid sees the white as background and the black as foreground. Which is strange since the alpha of the chroma keys in Avid are correct.

Invert Key selected in Matte Key.

Because of the way Avid looks at alpha mattes, select Invert Key in the Foreground effect parameter of the Matte Key. When you monitor V3, the result will look like the original chroma key. The difference being you are now free to add effects to the foreground track.

For this tutorial, we'll drop a Chrystal  and a Color Effect on to the foreground on track V2 . Using the Matte Key to do the composite instead of depending on the chroma key effect, allows you to manipulate the foreground without affecting the background.

This simple tutorial is intended to give you the basic concept of what you might be able to accomplish when you generate a matte key from a chroma key in the Avid Media Composer. I hope it is helpful in whatever application you may need.