Mastering Video Visibility with Luma Mattes in Your After Effects Projects

So in this lesson, we're going to look at how to use video as a luma mat. Another lesson, we looked at how to use the alpha mat, which is transparency. But now we're going to look at using the brightness of a video to control the visibility of another video.

This is the luma mats composition. I've already done the alpha mat previously. I'm going to close these two up and focus on just on the luma mat comp.

So there are three layers here. The first is the hoodie guy, luma. And again, this is just basically a regular video file.

This is not transparent. It's how the video was shot. The guy in this hoodie was against a white background.

Okay. Now for the record, this would have actually been an easier process. If the guy in the hoodie had had dark hoodie on, that would have actually made this a lot easier.

Or if they had shot the background as dark with the bright, bright, it actually makes it a little more difficult to do this, but it's still doable. It's still doable. Anything that has a variation in brightness is will actually usually work pretty well.

So hoodie guy, luma, abandoned boats is right there. And then landscape background is right there. Okay.

So what I want to do is basically have the abandoned boats use the hoodie guy, luma as a track mat. So I'll swap my layer switches. So my layer modes, little button at the bottom of the column, abandoned boats.

I'm just going to use the pick whip or the dropdown menu to pick hoodie guy, luma. And it's going to assign this luma in this case, that's the icon for luma. For the record, the icon for alpha using alpha from the layer is the little black circle in the white square.

Luma looks like that, like a sun brightness, which makes sense. Okay. And this is the inverted option would do that instead.

The reason our problem with this is there's not much contrast in the initial video. Okay. So I want to change that.

What I want to do is take this video. I'm going to pre-comp it because I have a feeling I'm going to want to do a couple of different things to this, including add some effects and maybe some of the graphics to it. So I'm going to pre-comp this.

The keyboard shortcut is command shift C on Mac control shift C on windows. You can also right click on the layer and choose pre-compose. Okay.

I'm going to move all attributes. In this case, there's no attributes assigned to this. It's not really going to matter.

And I'm just going to call that hoodie guy, luma comp. And I'll say, okay, so I'm going to go into this and do a couple of things to make this a little more, more variation in contrast. Okay.

So what I would like is to have him fully dark and the background fully bright. So the first thing I'm gonna try with that is an effect called threshold. If I have some presets, search for threshold, toss it on this layer.

And it gives me almost nothing of what I want. So I'm going to adjust the threshold level property. And as I pull it down, everything will get brighter.

As I push it to the right, everything gets darker. Now, my goal is something like this, where he's pretty much fully a silhouette. So somewhere around 200 or so, 225, I can't go too far cause it'll cut too far into him, but what I'm looking for is him to be pretty much a silhouette and everything around him to be white.

Now what this would create, if I go back right now, is that, so it cuts out here and here, so basically what it's using is all of the areas that are dark are now hidden on the abandoned boats comp. So I am going to invert that because really I want the boats to be visible inside of him, but my problem is when I go back to that Luma comp, because I use threshold, the background is also a problem. So here's what I'm going to do.

I'm going to take my pen tool, use my pen tool, I'm going to draw a little mask, quick mask around him. And he doesn't move, so I don't have to really do much with the mask, but I'm just basically roughly silhouetting him like that, so I end up with this. Okay.

Now I just want to make sure that the mask fully encloses him. So I'll just like play my timeline. It doesn't move very much.

The mask is not cutting him out. That's good. It's kind of just standing there, which actually works out pretty well.

Now, when I go back to my Luma matte video, this is what I have. I have like him visible, but I also have everything else around him hidden. So what I want to do is make the rest of his background, which is really just empty space.

I'll turn on my transparency grid option right there, white. So I'm going to go to layer, new solid. I'll make it a white solid.

So go to the color box, upper left hand corner is white, make it comp size. Okay. I'll put that behind him.

So now inside of my pre-comp, I have a mostly black silhouette of him and white space around him. Even though this is made from two layers in this pre-comp, in the Luma matte, it's looking at the entire comp area. So all it sees is black and white.

So again, if I were to turn back on this layer, this is what it would see. It doesn't care that in the pre-comp that's made from two different layers. It's irrelevant.