What does TrkMat mean in After Effects?

TrkMat is short for track matte, the Timeline column where you choose a layer to use as a matte; versions since 2023 label it Track Matte. The chosen layer's alpha or luminance decides which parts of the current layer are visible.

What is the difference between an alpha matte and a luma matte?

An alpha matte uses the matte layer's shape and transparency. A luma matte uses its brightness, so white areas show the target and black areas hide it.

I can't see the TrkMat column in After Effects. Where is it?

Press F4 or click Toggle Switches / Modes at the bottom of the Timeline. If it is still missing, right-click a column header and enable Modes.

Glossary

Track matte

Name: Premation
Author: Premation

Using one layer's luminance or alpha to decide another layer's transparency. A luma matte uses brightness; an alpha matte uses the shape.

Also called TrkMat, Track mattes, Alpha matte, Luma matte.

In After Effects

In After Effects it is the Track Matte column in the Timeline, shown with the Modes columns (F4 toggles Switches and Modes). Before After Effects 2023 it was labelled TrkMat and always used the layer directly above, with Alpha, Alpha Inverted, Luma and Luma Inverted options; since 2023 a pick whip chooses any layer, with Alpha/Luma and Invert toggles.

In Premation

The TrkMat column in the timeline, Properties ▸ Blending and switches, or Track Matte in the layer's right-click menu. Alpha, alpha inverted, luma and luma inverted.

Step by step

Put the matte layer (text, a shape or a gradient) and the layer it should cut in the same composition.
Select the layer that should be revealed.
Set the matte in Properties ▸ Blending and switches, in the timeline's TrkMat column, or from Track Matte in the layer's right-click menu.
Choose alpha, alpha inverted, luma or luma inverted.
Animate the matte layer's position, scale or shape to animate the reveal; the matte layer itself stops rendering on its own.

Tips

Use an alpha matte to fill type or a logo with video or texture; use a luma matte with an animated gradient for a soft reveal a mask path cannot draw.
Luma mattes read brightness: white keeps, black hides, grey is partly transparent. Check the matte's contrast before blaming the target.
If the matte layer shows up in the render, it is not assigned as a matte yet.
In Premation the matte does not have to sit directly above its target in the layer stack.

Read the docs: Masks and mattes

Questions

What does TrkMat mean in After Effects?: TrkMat is short for track matte, the Timeline column where you choose a layer to use as a matte; versions since 2023 label it Track Matte. The chosen layer's alpha or luminance decides which parts of the current layer are visible.
What is the difference between an alpha matte and a luma matte?: An alpha matte uses the matte layer's shape and transparency. A luma matte uses its brightness, so white areas show the target and black areas hide it.
I can't see the TrkMat column in After Effects. Where is it?: Press F4 or click Toggle Switches / Modes at the bottom of the Timeline. If it is still missing, right-click a column header and enable Modes.

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