How to Replace Your Sky in After Effects CC

After Effects 28/06/2019 4 min read

Replacing a sky in After Effects can be incredibly powerful when done correctly. It gives you the ability to either create an impossible world you’d never achieve in-camera or enhance your visuals, pushing them to that next level of quality. To keep things straightforward, we’re going to be sticking with a classic realistic sky replacement. Let’s get started!

How to Do an After Effects Sky Replacement

There are two basic scenarios you’ll regularly see when it comes to working with a sky. There’s the sky that’s totally blown out, and then there’s what we’re going to be looking at; sprucing up an otherwise reasonable shot.

Both of these situations can have multiple different approaches, but today, you’re going to learn how to tackle the first option. 

Step 1: Prepare your Clip

Firstly, you’ll need to prepare the clip you want to work with. To replace the sky, After Effects needs to analyze your entire clip, so it makes sense to trim the clip so you’re only using the section that will be seen.

  1. Drop your footage into a New Composition.  
  2. Drag the clip in the Timeline, so it begins with the part you wish to use.
  3. Place the Playhead at the point you want the clip to stop, and press N.
  4. Right-click on the work area bar, and select Trim Comp to Work Area.

Step 2: Track Your Scene

Now, it’s time to track your scene. The reason why is that you’ll need to inform the fake sky later on, how to move and react so that it looks like it’s really there. For example, if your scene wasn’t shot on a tripod, it would look out of place if the sky was still and the rest of the scene was moving.

  1. Highlight your clip in the timeline.
  2. Go to the tracker window. If your tracker isn’t there, go to Window > Tracker.  
  3. Select Track Camera. After Effects will begin the process of tracking all of the camera movement in your shot.
  4. In the Effects Control panel, select the Advanced drop-down menu, and check the Detailed Analysis box.

It may take a while depending on the length and quality of your video clip. Once it’s done, you should see tracking points around your footage.

Step 3: Choose Your Tracking Points

Next, you need to choose the tracking points that you’ll attach the new sky to. You’ll need to make sure the new sky moves with the scene, so you’ll need to choose tracking points that are a similar distance from the camera and are not moving independently. With sky replacements, it’s best to select the still points on the horizon.

  1. Select your tracking points by clicking and dragging a circle around them. If you’re having trouble selecting these markers, check to see if your layer controls are selected by going to View > Show Layer Controls.
  2. Once you’ve highlighted them, right-click and choose Solid and Camera. A solid will pop up attached to your tracking marks.
  3. Play the clip through to see how it moves with the scene. If you’re not happy with it, delete the Camera and Solid layers, select your clip, and repeat this step.

Step 4: Add the New Sky

Now you need to bring in the replacement sky image. Choose an image that suits your scene and has been shot from a similar angle as your clip.

  1. Import your image, and drag it to your timeline below your other layers.
  2. Lower the Opacity of the original footage, so you can see both at the same time.  
  3. On your new sky layer, select the 3D option.
  4. Grab the Pick Whip, and drop it on the Solid layer. You should now be able to see the new sky layer moving with the footage.

Pro Tip: If the solid layer is a little bumpy in its movement compared to the original footage, try moving it toward or further away from the camera using the Z position setting, and scale the footage to fit the frame.

Step 5: Removing the Original Sky

With the new sky is in the scene and following the camera movement well, it’s time to remove the old sky from the original clip.

  1. Raise your clip Transparency again to 100%, and turn off the new cloud layer.
  2. Search for the effect Color Range, and drop it onto your footage.
  3. Select the top Eyedropper and choose a very average part of your sky. You’ll see a large chunk of your sky is removed.
  4. Using the Eyedropper, continue selecting parts of your sky until it’s all removed. At the bottom of the effect, you’ll see sliders, and you can use these to finesse the look. Using fuzziness can also help to prevent pixelation and flickering due to the effect.

Pro Tip: Keep in mind that in a real horizon, you’ll get some natural fall-off where the sky meets the landscape, so your mask may not have to be completely perfect here depending on the footage you’re working with.

Step 6: Clean Up the Edges

The effect has started to come together, but it’s likely you’ll have other parts of your shot missing that don’t need to be. The edge between the original clip and the new sky might also be a little harsh. Fortunately, the cleanup method is quick and easy.

  1. Select the new cloud layer and create a Mask around the area you want it to show, giving it a small edge where it overlaps the frame and your horizon. 
  2. Increase the Feather of your mask, so that the edges between the clips begin to blend. That’s sorted the harsh line between the clips.
  3. Next, duplicate your original clip, and move the copy to the bottom of all your layers.
  4. From the duplicate, remove the Color Range effect. Now you’ll have three visible layers: your footage with no effects at the very bottom, your replacement sky with a mask in the middle, and your original clip with the sky removed on top.

Step 7: Color Correction

Finally, you’ve come to the all-important finishing touch that is color correction. For the effect to fully work, you’ll need the audience to believe that these two elements belong in the same world.

You have two options, you can adjust the new element to match the footage, or you can change the footage to match the new element or some combination in between.

  1. Right-click in the timeline and select New > Adjustment Layer.
  2. In the Effects browser, search for Lumetri Color, and drag it to your adjustment layer.
  3. Play around with the settings until you’re happy with how it looks.

Now you know how to replace the sky in After Effects in seven easy steps. As demonstrated in this tutorial, you can see the impact enhancing the sky can have on your finished film or video project. Now you know the essentials, try experimenting with your chosen background to see what new worlds you can create!

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