What is an Alpha Channel in After Effects?

When editing images in After Effects, the color information is stored in three main channels: red, green, and blue. These channels are combined to create an image in full color. So, what is an alpha channel in After Effects? Think of it like an invisible fourth channel, which saves any transparency settings for the image. Alpha channels also you to isolate a certain section of your frame and control its opacity, so it can be edited and saved for later use. After Effects allows you to save one alpha channel per image or clip, which is also known as an RGBA. 

Below, we'll show you how to export an alpha channel in After Effects, so that you can save transparency information, apply dedicated effects to that area, or layer multiple video clips in a creative way. This process can be used for photos and videos, but in this example, we'll be editing a hypothetical video of a tree being planted.  

  1. First, launch After Effects and import the video clip that you wish to edit. Now look in the Composition panel and find the Transparency Grid button, which looks like a rectangular checkerboard. When you click on it, the background should become transparent and be replaced with grey and white checkers. You should only see the tree. 
  2. Next, you'll need to add your edited composition to the Render Queue, so go to the Composition drop-down menu and select "Add to Render Queue" (you can also press Control+Command+M). Your new composition should appear in the queue near the bottom of your screen. Click on it to bring up the Render Settings, and select "Best" in the Quality section. Then, click OK.     
  3. Now, go back to the Render Queue and find the Output Module section, which is located below Render Settings. Select "Lossless with Alpha", and then click on it to bring up the Output Module Settings. 
  4. In this new window, you can select your output video format, with options like Quicktime, MPEG4, and H.264. Then, look at the Video Output section and make sure the Channels option is set to "RGB + Alpha", the Depth is "Millions of Colors+", and the Color is "Straight (Unmatted)". Click OK to apply these settings. 
  5. Finally, click on the "Render" button to save your edited RGBA video, with the alpha channel enabled and the background removed. You can re-import the rendered file and layer it on top of another clip to create special effects and cool edits, use the alpha channel to isolate your tree visuals for a particular scene, and much more!
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