Use of Mask
In After Effects, A mask can be used to crop something from our footage. Similar to Photoshop, where we use a Pen Tool to create a mask but since After Effects is all about Motion Graphics, cropping something is not that easy.
Since the object we want to crop can be in motion. We need to animate our Mask using Key Frames. Though this can also be achieved using the Rotoscope tool since it is automated, but one should also know the manual method since Rotoscoping tool can’t be used everywhere. Animating a mask manually frame by frame is a lengthy process and requires lots of patience.
How to Animate Mask
To create and animate mask using Key Frames. Go through the steps below.
- Click on the Pen tool or use the Keyboard Shortcut G to enable the Pen tool.
- Now draw a mask around the area you want to crop from your footage. Make sure you are the first frame on your timeline.
- Once you have created the mask. Click on the layer on which you created the mask and hit M on your keyboard to bring out the Mask options.
- Now click on the Stopwatch at Mask Path to setup a Key Frame at frame one.
- Use the timeline slider to move couple frames ahead. You will notice that your mask will start stay at one place while your footage is moving.
- Adjust the mask again using the vertices so that it properly aligned with the section of footage you want to crop.
- Again move few frames ahead and adjust the Mark accordingly.
- Do this until your Mask is completely animated throughout your Footage.
If you feel irregularity in Mask animation, you can adjust it anytime using the Mask vertices.