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Green Screen

By Tom Kirkman

Green Screen (or Blue Screen) is like a visiting relative who has lent you money: treat them carefully, respectfully, simply, even frugally and they'll disappear.

Witty intro aside we're talking about lighting, of course and the most frequently asked question is how to light the screen, right up there behind "should I buy blue or green?"

As for the blue/green question, that depends on your subject. Think in terms of opposites: if your subject has blue in it, use green and vice versa. If you shoot a wide variety of subjects, it really does help to have both.

That being said, while not always possible, it helps to use the color that is closest to your eventual background color. A blue sky, for example, would benefit from use of a blue background. This would serve to hide any blue edges that might appear on your subject as a result of imperfect masking.

The choices in the background material itself are myriad. At the entry level, Savage provides blue and green paper rolls in 53"x12 yards and 107"x12 yards, that won't break the bank at $21.50 and $39.95 respectively. Botero, perhaps the most affordable in fabric, offers 5x7 muslin backgrounds in blue, green or a reversible blue/green, that fold into a disc 1/3 their size. They also offer an 8x16' version, complete with a skirt for the floor to enable full-length shooting.

Photogenic produces a 57x77'; reversible popup while Lastolite weighs in with blue and green fabrics for their Skylite Frame/Panel systems in sizes up to 42x78.

Wescott’s popular Scrim Jim frame system includes a reversible Chroma-Key Blue / Green fabric for their largest (72x72”) frame.

Lastly, for permanent installations, Rosco will sell you enough chroma by the gallon to paint your world blue or green

Whichever you choose, two aspects are of paramount importance: the background's proximity to the subject and evenness of its illumination. While there's general agreement about at least 4-6ft background to subject distance, the reality is, further is better to control the spill of chroma light bounced onto the subject which would result in a dark matte-line around them once it's keyed.

While there's not much choice with papers other than to "slash and burn" and pull down some fresh footage, fabrics should be stretched taught and/or steamed to minimize wrinkles that would read as darker values. Evenness of illumination can be accomplished with almost any source from broad lights like Lowel's tungsten Tota, to studio strobe or even fluorescent fixtures, provided the proper light controls are used to eliminate detail in the background's surface.

You have a lot more freedom when it comes to lighting the subject itself, but be mindful of the light quality of the new background you're keying in. You want to avoid a subject ablaze in spectacular late day light against a cloudy-day background, as an extreme example. And you also want to avoid shadows from your key light falling on your carefully lit background.

Lastly, it's a good idea to be around during wardrobe or product choice time. Make sure that your subject colors are as disparate as possible in relation to whichever key color you choose, thus avoiding "digital holes" which can cause post-production delays.

While we've by no means exhausted the subject of lighting a keyed background, the above should be helpful in choosing a basic blue or green screen kit and addressing some basic procedure.

With very little outlay, you'll find the door open to a nearly infinite supply of background subject matter from stock agencies or your own travel photos. Once under way, most videographers and photographers consciously seek out scenes and situations to add to their growing library of images to be plucked at will and employed as custom backgrounds. If handled properly your portfolio will be peppered with big-budget style campaigns in exotic locales and you won't even have left your studio.

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