Requirements: Sufficient knowledge of PhotoShop and AfterEffects, understanding the principles of animation and different animation techniques. Timing.

We can use the layer immediately on top of any layer as a mask that only reveals parts of the underlying layer. This can produce some interesting effects. In the example below we will make a fire bird, using a greyscale animation sequence as a mask and a real fire sequence.

Below you can see thumbnails of the sample silhouette animation. The images are greyscale. The white pixels will be opaque and the black pixels will be transparent.

This is an image from our fire video:

1. Import the Fire.mov and the masking sequence in AfterEffecs:

Make sure that the mask is imported as a sequence, so that it appears as a single layer in the timeline.

2. Position the two footages in Timeline: mask on top, fire below it, like this:

And then choose Luma Matte from the Fire.mov pop-up. This immediately converts the layer above it into mask layer and displays on the stage only parts of the underlying layer, based on the method selected. There are two different methods and two "inverted" variants. The first is what we just chose - a greyscale image - you can think of this as of a separate or external Alpha Channel. The second method uses the actual Alpha of the masking layer. It's just a matter of preference or it can depend on the sources we have which masking method to choose.

The fire is instantly masked and looks now like this:

3. Give the fire a bit brighter look
Duplicate both the fire and the mask by pressing ctrl+D on the keyboard and then for the second instance choose Add as a blending method.

This makes the brighter zones even brighter and gives a real fiery look.

4. Final adjustments
You can apply any other effects that might make the animation look even more impressive.

What I finally did here was to Gaussian Blur the lower masking layer, so that it looks less cut-out. It gives us this nice soft glow effect around the edges.

You can use the same method to create interesting effects in many situations - revealing the next scene, display titles, texturize waterfalls, psychedelic tunnels, etc. More exciting stuff comes in the next tutorial.

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