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Creating Realistic Explosions in After Effects
Richard Lainhart on Wed, November 2nd 0 comments
Want to create Hollywood-style explosions as seen in your favorite action/thriller movies? Using After Effects you can and Richard Lainhart shows you how. Get ready to detonate...

In this Feature Tutorial, I'll show you how to create a common special effect in After Effects, one you've seen many times: blowing a window out of a building as if a bomb had gone off inside. For this tutorial, we'll just do a basic version of this effect so you can get an idea of how to put it together on your own. It won't be super-realistic, but you'll certainly get the idea. Let's get started.

Step 1 - Assemble Your Source Footage

To begin, you'll need some source footage to work with. I'll be using a still photo of a neighbor's house, which has nice big glass windows on the second floor, and an explosion sound effect from my own SFX library. In addition, we'll be using a piece of stock explosion footage from ArtBeats, purveyors of all kinds of digital stock footage. If you don't have access to a commercial stock library, there are also many free explosion clips available online you can use instead.

Step 2 - Create Your Explosion Composition

I'm going to be working at at a relatively small frame size of 640x480, just to save screen space, in a 7-second composition. Since this is an Intermediate tutorial, I'm going to assume you know how to set up a new comp and import footage.

Next, add your still image to the comp. This layer should run the entire length of the composition:

Add the still image to the comp

Step 3 - Mask the House Window

Next we're going to mask out the window in this layer (which will be the rearmost in our final composition) to create the effect of the blow-out window. Masking the window will create a hole in the layer through to the black background. So, double-click the house layer to open it in the Layer window, grab the Pen tool (G), and draw a simple 4-point closed mask with straight lines that outlines the window:

draw a simple 4-point closed mask with straight lines that outlines the window

Go back to your Comp window, open the Mask properties for the mask you just created, and click the Inverted button for the mask:

Invert the mask

You'll now see the house layer with the window masked out:

Window is masked out

Step 4 - Duplicate the House Layer

Select the masked layer and type Command-D to duplicate it. Select the upper or frontmost layer of the two identical layers, open up its Mask properties, and uncheck the Inverted button for that layer. If you turn off the visibility for the rearmost layer now, you'll see just the window isolated on its own layer. This is the layer we're going to blow up to reveal the empty hole behind it:

Set up the layer to blow-up

Step 5 - Apply Shatter to the Isolated Window Layer

The After Effects Shatter plugin's whole purpose in life is to blow things up, so that's what we're going to use here. With the frontmost masked window layer selected, choose Effect > Simulation > Shatter. In the Shatter Effects Control window, the first thing you should do is set the View pop-up menu to Rendered (which will show you the final results, rather than just the wireframe of the shattered pieces), leaving everything else the same, and preview the results:

Even with the default settings, that's pretty cool, although it obviously doesn't look like a real window explosion (but you can see where we're going with this, at least). Next, let's tweak Shatter's settings to give us more realistic results.

Step 6 - Adjust Shatter's Settings

Now, this tutorial isn't really the place to go into Shatter in-depth, but fortunately we don't have to do too much tweaking to give us good results. First, open up the Shape properties in Shatter's Effects Control window and choose Glass from the Pattern menu; this will give us more irregular, realistic exploded shapes, rather than the default blocks. 

Next, set Repetitions to 200 or so, which will give us much smaller chunks, more appropriate to the relatively large size of the window. Finally, set the Extrusion Depth to 0.05, which will reduce the thickness and hence the overall size of the exploded chunks. At this point, your Shatter settings should look like this:

Shatter settings

and your previewed movie should look like this:

Much better! However, the explosion is a little slow right now, so we're going to do two more tweaks before moving on. First, open the Force 1 properties and set Strength to 15, which will blow the shattered chunks out faster:

Increasing the strength of Force 1

Next open the Physics properties and set Gravity to 6, which will help pull the chunks down a little faster after they're blasted out.

Set the Gravity properties to 6

Step 7 - Delay the Explosion

As you've no doubt noticed, the Shatter explosion starts right at the beginning of the layer, which it always does. I'd like to delay the explosion a little, though, so it doesn't start right at the beginning of the final clip. There are a few ways to do this, but with this material, a simple way is to just move the Shatter layer a little later in time and add another copy of the still image at the beginning of the comp to make up the time. So, just drag the Shatter layer in the Timeline so it starts at 1:00 (or wherever you like), then drag another copy of your still image into the Layer window so it starts at 0:00. Next, trim the end of the new layer so it ends at 1:00 by dragging on the end of the layer in the Timeline. The first few seconds of your comp Timeline should look something like this:

delaying the explosion

And a preview of the first four seconds or so should now look like this:

Step 8 - Add the Explosion Footage

Now, of course, we need to composite our explosion stock footage into the scene so we have something to blow out the window with. It is possible to simulate explosions with particle systems in After Effects, but you're almost always going to get better results with a real explosion, which is what we'll use here (it's also a lot less work).

Here's the one I'm going to be using:

As you can see, it's shot against a black background, and the explosion stays completely within the frame, so its edges don't get cut off, both of which will make this clip particularly useful in this context.

So, drag it into the comp and position it between the Shatter layer and the masked background layer. We want the explosion to appear behind the shattered window layer but in front of the blown-out window layer. Then drag the footage in the Timeline so its beginning lines up with the beginning of the Shatter layer.

Step 9 - Screen the Explosion Footage

With this footage, the first thing we need to do is remove its black background so we can composite it in the scene. We could try keying, but there's a simpler way: Screen Mode. So, reveal the Blending Modes column in the Layer window, and set the explosion footage layer to Screen, which will knock out the black background and leave only the brighter explosion pixels behind.

Set the footage layer to Screen

Step 10 - Position and Scale the Explosion Footage

At this point of course, the explosion is centered in the frame and nowhere near the window. So let's just drag it in the Comp window until it's centered in the empty window frame, adjusting and previewing as needed so the explosion itself appears in the correct position. With this particular footage, we also need to scale it (in my case, to 80%) so it fits a little better in the scene and doesn't overwhelm the shattered window chunks. You may also want to adjust the start point of the explosion footage layer slightly so it lines up better with the start of the Shatter explosion. This will depend on how your own stock footage begins, of course. A quick preview, and here's where we currently stand:

Step 11 - Apply Levels to the Explosion Footage

We're almost done, and have just a couple of tweaks to do to complete our tutorial. First, you'll notice that the explosion footage looks a little washed out and thin, which is the result of applying Screen to it. So, with the layer selected, choose Effect > Color Correction > Levels, which will let us brighten up the footage a bit and strengthen the effect. 

In the Levels Effect Controls window, drag the right-hand arrow under the Histogram towards the left, which will have the effect of brightening and increasing the opacity of the footage while still keeping the black background transparent. Here's a shot of my settings, although yours of course will depend entirely on your footage.

Adjusting the levels for the explosion

With the right Levels settings, your footage should look something like this: much solider and more powerful.

The image with better level settings

Step 12 - Add an Explosion Sound Effect

The final step is to add an explosion sound effect to help sell the shot. I found a good one with falling debris in my SFX library, but you should be able to find a free one for yourself online. Once it's in the timeline and lined up with the explosion visuals, a quick render gives us this:

And there you go! As I mentioned, this is a basic tutorial to introduce you to creating these kinds of effects. Refinements on the technique might include adding a camera shake during the explosion, working with handheld footage and motion-tracking the explosion in, adding more layers of Shatter and explosion stock footage to add complexity to the effect, and so on. But this should get you started, at any rate. And as always, I encourage you to experiment with what you've learned here and above all, have fun.

Want to learn more about Adobe After Effects? Jump straight into these After Effects tutorial-videos!

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