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Making a Track Matte with a changing pattern behind it

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Matt Green
Making a Track Matte with a changing pattern behind it
on Aug 18, 2012 at 9:28:32 pm

I'm doing a small project where I'm rotoscoping (really basic - using the paintbrush to draw over a video frame by frame). I've been trying to put a moving pattern inside the shape of someones face kind of like what happens at 33 seconds in this video:

I've been told that a track matte is the way to go but I'm not sure exactly what that is or how to go about executing it. I couldn't find any really basic tutorials or places to start.

Any guidance would be greatly appreciated.

(I'm relatively inexperienced with AE and apologize if this is a dumb question.)

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John Cuevas
Re: Making a Track Matte with a changing pattern behind it
on Aug 18, 2012 at 11:35:39 pm

A Track matte is where you have a layer used the layer above it to determine what part of the layer will show through.

Create a solid and add the effect Generate ->4-color gradient effect to it. Now add use the text tool and make any text, make the text the top layer. Now use the TrkMat pulldown and choose Alpha Matte(if you don't see the track matte pulldown, press F4 or right click in your timeline and go to Columns -> Modes). Your solid layer will now use the alpha channel of the text and only show up there. If you choose alpha inverted, where there is text the gradient won't show up.

You also have luma and luma inverted. This check the lightness of the level above and uses those pixels for to show what will show and won't show. So add a the effect Generate -> Gradient to your text and choose the luma track mattes. Now your gradient layer should gradually fall off as the layer goes from white(bright) to dark(black).

Here is a project where illustrating the above technique:

Also being new you probably would benefit from working your way through the Video Copilot Basic Training series, Number 4 covers track mattes.

Johnny Cuevas, Editor

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.

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