Cut people or things out of your footage in After Effects with rotoscoping.
You thought you got the perfect shot for the ending of your post-apocalyptic wasteland rom-com — until you looked at the footage later and saw the pizza guy drive though the background. Thanks to rotoscoping, all is not lost!
Create Solid Layer
First, create a solid layer (CTRL-Y) of the same dimensions as your footage, and place it above your footage. The color does not matter.
Turn down the opacity (T) of your solid layer so that it is at least transparent. Mask/path visibility should be enabled by default, but you can ensure it is by checking the Toggle Mask and Shape Path Visibility button seen below:
Select the Pen Tool from the task bar or by pressing G.
Navigate to the first frame that you want to modify, then begin drawing a mask around the edge of the subject you want to cut out.
If the shape you’re cutting will become more complex later on, you’ll want to add some extra vertices now to prepare in advance. Ensure that you complete a closed shape by connecting your final point to your first.
Once your mask is completed, click the keyframe stopwatch to enable keyframes. Proceed to the next frame and adjust the points of your mask to again match your subject. Each adjustment will automatically create a keyframe.
Note that as with any other keyframes, you can skip individual frames and allow After Effects to fill in the gaps. This won’t always be perfect, but it can save you a lot of time with simpler movements and shapes. Continue this process until the last frame you plan to adjust.
In some situations, such as rotoscoping hair, you may want one part of your mask to have a slightly blurred edge. Or, you may find that the outline of your subject becomes significantly more complex for a few frames or so.
Simply add a second mask to the same layer and repeat the same steps to keyframe it — only this time, you’ll want to keyframe the second mask’s opacity (not the layer opacity) to 0% when you want it to disappear. To soften the edge of a mask, increase its feather. You can access mask properties by selecting a layer and double-tapping M.
Use Layer as Alpha Matte
When your mask is ready, turn your mask layer’s opacity back up to 100%. Select your footage layer and make sure it is directly below your mask layer. Change its Mode to Alpha Matte, and it will use the layer as a mask.
Your subject should now be properly separated from your source footage. You can complete this step early in the process if you find it easier to work with. While a mask can be drawn directly onto a footage layer, a separate solid layer allows for a lot more flexibility.
With the ability to rotoscope, you can suddenly do a lot more with live action footage.
What tricks speed up this process for you? Let us know in the comments below.