this iMovie plug-in is billed as the “best-of-class compositing ('blue-', 'green-screening') plug-in”. but what does it do? simply Put, it allows you to intelligently blend two movies dynamically. this usually involves much more than using simple transparency masks because it allows you to target any color in one of your movies and make that color transparent. in tv, the color usually replaced by a picture usually is blue or green, hence the name 'blue/green screening' (the actor stands in front of a blue or green screen). the best known (and probably most often) example for this technique is the newscaster in front of the white house. the Process of intelligently combining two picture sources is also sometimes 'compositing'. the technique of replacing a key color with a whole picture is also called 'chroma keying'.
features
opacity slider
this controls the overall opacity of the effect, allowing you to blend the result back with the original effect (this is required for some advanced masking. don't worry if you don't need it).
configure dialog:
red source rectangle
this rectangle defines the area that will contain the second source (a movie or picture). all compositing is limited to this area. to re-size the rectangle, click and drag the handles. to re-position, click and drag inside the rectangle.
chroma key color
when using arbitrary color keying, this defines the color that will be regarded as invisible (= white color in the mask).
movie button
click into either to assign the second source. you may use any movie or picture format the Mac knows. if you use a picture with an invisible color, the invisible parts will be filled with the ‘background’ color (see below).
keep prop’s
if this box is checked, re-sizing the red still source rectangle will force it to have the same proportions as the original picture/movie.
