The single most important aspect of ‘pulling a clean key’ is lighting. The lighting should be even and diffuse. Bright ‘hotspots’ and shadows create different shades on the wall, and overexposed areas lack sufficient color for clean keying. (It is not how much light you have on the key wall, but how evenly lit that wall is.) Naturally, you want to keep your green (or blue) screen clean and free of wrinkles, ripples, folds, tears, or other blemishes, as well.

Second, the distance from your talent to the screen behind can make a profound difference in key quality. When the subject stands too close to the key colored background, the key color reflects back onto the subject, creating a green or blue fringe that is difficult to remove. If you have available space, move your subject farther away from the wall.

When good distance is out of the question, you can improve things somewhat by placing lights above and behind the talent, lighting them from behind with a complimentary color filter over the light to ‘cancel out’ unwanted reflection (for green use a magenta filter; for blue, orange or amber.

Don’t overdo back (or top) lighting, however. The limited dynamic range of the camera means there will be little useful color data in badly over-exposed highlights.  This can make it next to impossible to separate fringe zones (such as hair detail) from the background (especially when this is also overexposed).

Section 13.6.1

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