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How to Use Alpha and Luma Mattes in After Effects

In this lesson from After Effects for Beginners, with David Bode, you'll learn about alpha and luma mattes, and see an example of how each are used.

To follow along in this lesson make sure to open up the Mattes.aep file included in the downloads for this course. It will give you a project that looks something like this:

open mattes projectopen mattes projectopen mattes project

Some assets showcased in this tutorial will need to be downloaded from Envato Elements. Here are some links to stock videos and editable video templates to get you started:

What is a Matte?

Matte is an abbreviation for track matte, and that's when you use another layer to drive your target layer's Opacity. We're going to dig into the mechanics of how mattes function, and then we'll get into how to use them.

To help explain let's jump into the Alpha MATTES composition here and I'll walk you through what is going on. At the bottom of the layer stack we have a green solid.

green solid layergreen solid layergreen solid layer

I'll just solo that out there as you can see it's nothing special, just a really bright green solid.

solo the green solid layersolo the green solid layersolo the green solid layer

Above there is a layer named Pattern and this is a solid layer with a couple of effects applied to it. It has a a Fractal Noise effect, and a Colorama effect, which is what is generating the pattern shown.

pattern layerpattern layerpattern layer

This pattern layer is getting all of its transparency information from the layer directly above it and that's because it's set to Alpha Matte.

alpha mattealpha mattealpha matte

If I set this to no matte, you can see that it looks different. This is what the layer actually looks like.

pattern layerpattern layerpattern layer

But when I apply a Track Matte and set this to Alpha Matte, it's going to be using the alpha information, which is the transparency of the layer to drive its transparency.

Let's take a look at this matte layer right here and solo it.

matte layermatte layermatte layer

Info Inspector

Let's also take a look at this info panel which is usually located on the top right of the screen. You'll notice right here we have a little column R,G,B, and A. This stands for red, green, blue and alpha. The alpha channel is that pixel's transparency.

info panelinfo panelinfo panel

Hover your mouse over your composition, and you'll see that those numbers will dance all over the place.

255

The thing that I want you to look for right now, is the number for the alpha channel. As you hover the mouse over this rectangle, you'll see the alpha channel is reading 255.

alpha channelalpha channelalpha channel

And that's because right now this project has a bit-depth of 8-bits. Each channel only gets 8 bits which means 256 values. Now you may be wondering why the alpha is reading 255 and not 256, and that's because that last value there to get us to 256 is zero so it starts at zero and it ends at 255. This means that anything that reads at 255 is fully opaque, it does not matter what the color is. The color makes no difference to the value shown.

bit depthbit depthbit depth

You can change the color to anything you want as long as this rectangle has 100% opacity it will be doing the same thing.

Now in this larger rectangle here has a gradient. Open that up and select it.

select the large rectangleselect the large rectangleselect the large rectangle

Then open up the fill so you can see how the gradient is working going from red to black. But again the color doesn't matter because this layer is set to alpha matte, which means it's only looking at the transparency.

gradientgradientgradient

So in this gradient the opacity for the gradient has been set on one side to 0 and on the other side to 100%.

Hide the Matte Layer again so you can see the image, and play about with the color values. You'll notice that nothing changes.

play with the colorplay with the colorplay with the color

Now start changing the opacity, and you'll notice that the image starts to change. So when your fill layer is set to Alpha Matte or Alpha Inverted, it's getting all of it's transparency information from this layer's transparency, not it's color information.

play with the opacityplay with the opacityplay with the opacity

There is two ways to set this up. You can set it to regular alpha matte, or you can set it to alpha inverted matte, which is the exact opposite. It's as if I rebuilt this layer but I flipped all the opacity values.

How to Use Luma Mattes

Let's look at another example. In this Luma Matte's composition, we basically have the same three layers. However the pattern layer has been set to Luma Matte so it's going to be getting its transparency information from the luminescense of the matte layer directly above it.

select lumaselect lumaselect luma

And if we solo that, you can see that this time it's been set up to be black and white. That's because things that are fully white (which will be read as 255, 255, 255 in the reading panel, which means that it is fully white) will be read as fully opaque when things are set to Luma Matte.

matte layermatte layermatte layer

Things that are black are fully transparent. You can see that the gradient goes from black to white here, and that is what is being reflected with the pattern layer here.

pattern layerpattern layerpattern layer

Alpha Matte Project Example

Let me show you an example of how you might actually use Alpha and Luma Mattes in some real projects. Let's jump over to the Louvre composition.

project exampleproject exampleproject example

Now, in order to create this look, I'm using an alpha matte. So what I have going on here is a background layer which is a video clip with some effects applied to it.

alpha mattealpha mattealpha matte

I have a curves effect which is darkening it.

curves effectcurves effectcurves effect

I have a third party effect from Red Giants Universe called RGB separation, which is giving it this cool RGB split effect here.

rgb split effectrgb split effectrgb split effect

And then I'm using a Gaussian Blur to blur it out. 

gaussian blurgaussian blurgaussian blur

On the layer that's directly above it, you can see that there is a track now applied which you can also see just to the left of the layer name here. Those little icons indicate that this has a track matte applied.

track matte icontrack matte icontrack matte icon

If I set the track matte to None and the blend mode to Normal, you can see it's just the same, exact footage layer as the one below.

change track matte and blend modechange track matte and blend modechange track matte and blend mode

When I set the layer back to Add and Alpha Matte it's going to be using the layer directly above it for its transparency, and in this case that is a text layer.

So that is what is doing this 'word cut out' effect here. It's just a simple text layer and an alpha matte.

change blending mode and track mattechange blending mode and track mattechange blending mode and track matte

Another Project Example

Let me show one other example here and walk through how it works. Right here I have a pre-comp called waves.

waves pre compwaves pre compwaves pre comp

If I double-click on that we can jump inside that pre-comp and it's here I have a footage layer with a couple of effects applied to it. It's set to a blending mode of multiply.

project layout and effectsproject layout and effectsproject layout and effects

Below there I have this paper texture layer.

paper texturepaper texturepaper texture

And the idea is I just want some of that paper texture to show through on my footage layer.

subtle paper texturesubtle paper texturesubtle paper texture

If we jump in the Ink_Matte_2 comp, you can see that this is just a comp made of a bunch of ink drop elements that I found at Envato Elements, and I've arranged them to get this effect where it looks like the ink is bleeding from the center and expanding outwards.

ink matte compink matte compink matte comp

Now, all of these layers, if I double click on one, it will bring it up in the layer viewer here. All these layers are black and white. But I'm combining all of these to use as one matte.

combining the ink spotcombining the ink spotcombining the ink spot

This is done by setting all of these layers here to Multiply, and then having a white solid on the background. So it's essentially compositing them all on top of each other, and the effect is that I get one pre-comp that's just black and white, using the ink matte as a track matte.

background and multiply layersbackground and multiply layersbackground and multiply layers

In this particular case, it's set to Luma Inverted Matte. And that's because all of those ink drops are essentially backwards for what I need. If I set this to Luma Matte, it does the opposite.

luma matteluma matteluma matte

Congratulations

Congratulations! And that's how you can use mattes for animation and to improve the look of your projects. Now that you've learned the basics, check out some of the other tutorials we have on Adobe After Effects below.

I hope you've found this tutorial useful and I'll see you next time on Envato Tuts+!

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