Track mattes define the layer’s visibility according to the previous layer/the layer on top.
To find them you need to click on Toggle Switches for 4 columns to appear:
Mode | T | Track Matte | Parent
There are two kinds of track mattes:
Luma and Alpha
- The Alpha matte, as the name gives away, uses the layer’s alpha channels to pick what can or can’t be visible.
So let’s say we want bananas to be coming out of the gramophone’s horn.
You create a shape layer of the place that you want to contain the bananas
Put the layer over the bananas layer then select alpha matte from the track matte list.
It pretty much works the same way a clipping mask would work in software like Photoshop or illustrator.
If you select Alpha inverted matte, the shape layer works the opposite way: everything but that shape can contain the bananas layer.
- The Luma matte uses black and white:
Everything white is visible, everything black is invisible, and all the 50 or more shades of grey differ in-between both visibilities.
Duplicate the gramophone’s layer; go to effects – Black & White from the effects and presets panel. Here, the changes depend on the colors present in your footage, picture. My goal is to write “Luma” behind the pink horn, so I’ll need to isolate the background from it.
By adding a maximum of red, the red colors become white while reducing the blues and cyans (other major colors in the picture) you create a more pronounced contrast of black and white.
Write “Luma” in a text layer, and place the black and white layer on top of it.
Your layers should be in this order:
Select “Luma inverted layer” and then let the track matte do its thing.