What is Green Screen?
The Green Screen tool allows you to cut out objects from videos, a process known as rotoscoping. This common task is the bread-and-butter of video manipulation. Once you have cut an object out of your video, you can swap the background, display text behind it, or even selectively apply visual effects to the region.
Most tools for rotoscoping require painstaking frame-by-frame edits by manually highlighting the border of objects. With Runway, you can create professional masks and cut object from videos with just a few clicks. Here are the steps to get started...
Step 1: Choose your clip
Open Green Screen by clicking on Video Tools under the media sidebar. Now select an asset by opening the Assets sidebar. All of your exports from other Runway tools appear here. If you want to use an asset from your computer or external software, you can simply drag and drop onto the interface to get started.
Our tool is designed to track individual objects throughout a scene. If you have lots of footage to cut, it's best to trim into clips with relatively consistent camera angles and lighting conditions, and then edit each one with Green Screen individually. If you want to track two separate objects in the same video, we recommend you use Green Screen twice to track them separately.
Step 2: Click to create keyframes
To start off the process, seek to an initial frame which contains the desired object in clear view. Then click on the object in frame to create your initial mask.
The toolbar above the timeline allows you to switch between Include clicks which expand the mask to the clicked location and Exclude clicks which retract the mask. You can also swap between Foreground and Background to see what the masked object looks like.
Now that you have an initial mask, you can click Preview to see the expected result if you were to propagate the mask to the rest of the video. You can also click on the timeline or use the arrow keys to check the results on a frame-by-frame basis.
You'll notice that there are regions of video where masking can be improved. The goal is to create a set of keyframes from which Green Screen can estimate the mask for the whole video. A new keyframe is usually needed when the target appearance changes (e.g. a body part appears for the first time, the subject moves to a different background, or lighting conditions vary).
Now you rinse-and-repeat, creating keyframes where the current results are lacking, and then previewing the updated results. Depending on the amount of movement and background complexity, Green Screen may need just a pair of keyframes for the entire clip, or it may require one keyframe every few seconds.
Step 3: Export your result
Once you're satisfied with the mask, click Export to output a video file. You can change the name of the video, and select a chroma-key background.
The output will appear in your Assets, from which you can export the file into other software to add visual effects.
Bonus: Composite text with iMovie
Using our exported file in any video editor or compositor is quite easy. Here we use iMovie, but similar effects can be achieved with most video software.
First, place the desired text on top of your source video. Then, import the output from Green Screen into iMovie and place it on top of the desired text. By applying a the green-screen effect, as shown here you can overlay just the subject on top of the text.
Congratulations, you've just done your first Green Screen!
If you have any questions or feedback, let us know! We can't wait to see what you create.