You can record video in front of a green or blue backdrop, and then “cut out” the subject and superimpose it into another video clip. This is called a “green-screen” or “blue-screen” effect. For example, you could record a friend acting scared in front of a green or blue backdrop, and then place that video into a video clip showing an angry bear, so that your friend appears to be standing, terrified, next to the bear.
You can also drag the green-screen or blue-screen clip over a solid-color or animated background clip.
If the subject of your video is green or is wearing green, you should record in front of a blue background. Likewise, if the subject of your video contains blue or is wearing blue, you should record in front of a green background.
To use the green-screen or blue-screen effect:
Record video in front of an evenly lit, solid bright green or blue backdrop, and then import it into iMovie.
When you record, do the following for best results:
Use a pure, highly saturated color of green or blue for the backdrop. For paint and cloth, the best green to use is often called “chroma key green.” The best blue is “chroma key blue.”
Make sure the subject of the video isn’t wearing anything green if you’re shooting against green, and don’t include anything green in the shot other than the backdrop. The same applies if you’re shooting against blue: the subject of the video shouldn’t be wearing anything blue, and there should be nothing blue in the shot other than the backdrop.
If possible, use multiple lighting sources to eliminate shadows on the subject being recorded.
Record a moment at the end with the subject out of the frame. This indicates to iMovie what should be cut out when the video is superimposed.
Make sure Advanced Tools are turned on.
Open the project you want to add the green-screen or blue-screen effect to.
In the Event browser, select video (a frame range or an entire clip) that you recorded in front of the green or blue backdrop.
Drag the selection directly over a clip in your project—it can be video, a solid-color clip, or an animated background clip—and release the mouse button when you see a green Add (+) symbol.
In the contextual menu that appears, choose Green Screen or Blue Screen.
The green-screen or blue-screen clip appears above the video clip in your project, as shown below.
You can drag it to a different spot within the clip, or to a different clip, to reposition it. You can also drag the ends to lengthen or shorten it. To drag an end, move the pointer over it until the pointer changes to a resize pointer, and then drag.
To more effectively mask areas of the green-screen or blue-screen clip, click to select the clip in your project (so that its border turns yellow). In the viewer click Cropped, and then drag the handles at the top or bottom of the viewer to more tightly enclose the subject of the video.
Anything outside the highlighted area in the green-screen or blue-screen clip is removed from the picture. Be sure not to crop out areas that the subject moves into at any point during the green-screen or blue-screen clip.
To produce a better-quality effect, double-click the green-screen or blue-screen clip in the Project browser to open the inspector, and then select “Subtract last frame.”
This action works only if you’ve included a moment at the end of the green-screen or blue-screen footage with the subject completely out of the frame.
Play back the effect by placing the playhead (the red vertical line) anywhere before the blue- or green-screen clip in the Project browser and then pressing the Space bar.
Press the Space bar again to stop playback.
To delete a green-screen or blue-screen clip:
Click to select the green-screen or blue-screen clip in the Project browser (so that its border turns yellow), and then press Delete.
Sound from the original clip and the sound from the green-screen or blue-screen clip play simultaneously. You can reduce the volume of either clip so that sound from the other clip stands out. Go to this topic to learn how: Reduce the volume of competing audio clips.
You can edit green-screen or blue-screen clips the same way you edit standard clips in your projects. For example, you can trim them using the Clip Trimmer, adjust their audio and video, crop them, and add video effects to them. You can also reposition or trim them using the Precision Editor.
If a green-screen or blue-screen clip covers a transition in your project, the transition doesn’t play.