By Stephen Schweickart Print Article
So you watched some behind the scenes footage from a Hollywood blockbuster and you noticed the gigantic blue or green walls they film against. You may already know that they do this so they can easily remove the color in post production and superimpose the characters onto a different backdrop, but what you probably don’t know is why they use both green AND blue and not just one or the other. I’ll try and demystify this so whenever you want to insert yourself into a pool party with a bunch of supermodels you can do so properly.
Let me play captain obvious for a minute and tell you the most straight forward reason to use blue or green. You don’t want to shoot on a blue screen if there’s a blue object in your scene, and the same goes for green. Seems like common sense, right? If your talent is wearing a blue shirt in front of a blue screen, you’ll remove the shirt, and not in a fun way. You’ll be stuck with a floating head as your main character and likely that’s not what you’re looking for, unless you’re trying to be a silly weatherman. You can get around this a little, but stick with this rule of thumb for now since you’re just getting started: If there’s blue in the scene, shoot on green. Easy peasy.
Now let me give you one that’s less obvious—time of day of your scene. If you’re planning to put your characters into a scene taking place during the day, shoot them on green. Why? Because getting a perfect key in post production is very difficult for even the pros, and in a daytime shot, any edges of leftover green will be far less noticeable. The same goes for night and a blue screen. You’d be able to see green spill plain as day in a nighttime shot, but the blue will be masked by the bluish tinge of the moonlight.
One final thing to keep in mind when picking your backdrop color is how much space you have. Green is the spilliest color out there because of how bright it is so it’s real easy to accidentally have your background color spill onto your talent and that can play havoc with your keyer in post production. Edges of your talent can easily be lost if you aren’t careful, especially with hair. Make sure that you have enough space between your talent and the green so that you keep as much of the green spill off of them as possible or you might jump off a bridge in frustration before you even finish your piece.
There are more advanced reasons to choose one color over the other, but these simple rules should get you through the chroma keying battlefield with only a few bumps and bruises.
Stephen Schweickart is the co-founder of VScreen. For more information on this topic visit VScreen’s site at http://www.vscreen.com/video101.html.
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