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Chapter 14. Effects in Action > Using Matte-Based Keys - Pg. 664

Effects in Action · Shoot using the best format possible. For video, choose a format with the least compression and the greatest color depth. 664 · Use a high-quality bluescreen. A good bluescreen should be painted with paint specially formulated for bluescreen work. If possible, use a shadow-free cyclorama, a background constructed from hard materials with rounded corners, to prevent shadows. · Use good lighting techniques on the set. Preferably, work with someone experienced in lighting an evenly lit, shadow-free bluescreen. Use lighting to help separate the subject from the background and reduce spill (blue light reflected on the subject). · Use a high-quality capture device. If possible, transfer the footage uncompressed, using a high-quality transfer method, such as SDI. · Doing good bluescreen compositing is harder than it sounds. You may need to use software dedicated to the job, such as plug-ins like Ultimatte's Primatte keyer or the Keylight plug-in found in After Effects' Pro- fessional. Using Matte-Based Keys Matte-based keys use an external image to define transparent areas of a clip. A typical matte is a high-contrast grayscale image (sometimes called a high-con ). You might think of it as an external stand-in for a clip's alpha channel. As in an alpha channel's grayscale, brightness in the matte corresponds to opacity in the foreground clip, so that white areas specify opacity, and black areas define transparency. The matte itself never appears in the final output; it only defines the opaque and transparent areas of the foreground clip, sometimes called the beauty . Sometimes the matte perfectly matches the shape of the beauty; other times, the matte cuts a shape out of the beauty (Figure 14.41,14.42 and 14.43). However, the image