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A compositor program is a video editing program that works with green or blue screens — or with raw film — to add special effects to the footage. While commonly seen in movies to create dazzling effects, compositor programs are more often used on TV shows and news and weather broadcasts. By replacing every pixel of color from the green or blue screen with another image, it appears to the audience that a weather broadcaster is in front of a weather map, when he or she really is against a blank background. Rotoscoping tools, which take a character or object from one scene and seamlessly transplants it into another setting, are often found in a compositor.
Whether someone is watching a movie, TV show or a news or weather broadcast, there will likely be some instances of compositing going on. The main principle of compositing is to take two or more image sources and combine them. In the most primitive sense, this is done by shooting actors or actresses against a green or blue screen. The compositor software understands that the green or blue screen in the undesirable color, so it blocks out all pixels of that color and transplants another image into its place. A problem with using this screen is that, if someone is wearing clothing in that shade of blue or green, the program also will transplant the background on top of the actor or actress.
The special effects created by a compositor may be dazzling or mundane. For the mundane aspect, a weather reporter will appear in front of a weather map or an actor or actress will appear as if she is in a different environment. Dazzling effects can be achieved by filming the tops of buildings, filming someone jumping from building-like fixtures in a green- or blue-screen environment, then combining the two to make a believable scene. Most compositors also generate special effects, such as balls of light with the light curving around surfaces, and give artists the ability to transplant graphics or animation into the video media.
Sophisticated rotoscoping, especially with modern compositor programs, is a simple feat. When someone rotoscopes, he or she adds one section of live film over another, such as taking one shot of a character and transplanting it over background footage or footage of other characters. The user just selects an area, without the need of a green or blue screen, inserts the secondary footage, and the rotoscope is complete.
What separates a good compositing job from a poor one is color control. The rotoscoping and special effects may all be done correctly but, if the color is off, the audience will see through the effect. This means program users have to expertly perceive color and know how to tweak the saturation and hue of colors until it looks authentic.