How to Shoot the Perfect Green Screen Video
Green screens are used to create background scenes and realistic environments without having to film on location. If you have ever tried to shoot a green screen you know it can be tough. If you don’t do it right it can be impossible in post production but if shot correctly you’ll have smooth sailing.
Below we are going to talk about how to make and use a green screen in your own but professional way when shooting your projects.
Check out the video tutorials below to get an instant overview of the process:
Green Screener: Put Your Light Meter To Shame On Green Screen
The good folks over at Hollywood Camera Work has created the Green Screener App, a revolutionary new tool that helps you get stunningly perfect green screen.
Green Screener App does away with light meters and waveform monitors, and SHOWS you exactly how even your green screen is, giving you the power to do literally perfect green screen (and blue screen) using just your smart phone or tablet.
Whether you’re working on a $100M blockbuster or you’re doing green screen in your basement, the quality of your green screen will dramatically improve with Green Screener App.
Check out the video below.
What exactly does Green Screener measure?
Put simply, it takes your device camera and breaks the green channel (or red, blue or luminance) into 4, 8 or 16 bands. We correlate that to roughly 2-Stop, 1-Stop or ½ Stop resolution between the bands. This article explains the correlation.
F-Stops Don’t Really Matter
The rule of thumb in the industry has been that green screen should be even to within 1 Stop of difference on a spot meter. That’s not terrible advice, although it’s not really accurate. But let’s first take a moment to appreciate that the person responsible for shooting the green screen is the Director of Photography, and since his tool is a light-meter, the advice has been given in light-meter terms.
In reality, the keyer doesn’t know anything about Stops, all it sees is RGB values (256 levels in 8-bit color spaces), and all it cares about is the difference in RGB values. Ideally, we’d like there to be less than 32 RGB values (1/8th of the range) in total variation. This is the real absolute.
Defining A New Standard
The 1-Stop rule evolved because the only tool we had was a light-meter, but in reality, it’s vague. However, it has value if it’s a standard that everyone has calibrated around.
In the same sense, 1 Band on Green Screener doesn’t correlate directly to anything, it’s simply 32 RGB values of an average 6-Stop video camera, but in time, it can become something we calibrate around.
Where before you might have said “If I’m within 1 Stop, I know I’m good”, with Green Screener you might learn to think “If I’m within 1 Band on Mid, I know I’m good”, and in time, that thinking starts to mean something.
Because Green Screener isn’t completely accurate in a scientific F-stop sense. It’s simply RELIABLE in what it does, and it represents what a keyer sees much closer than a light meter or a waveform monitor.
To add one more piece to the puzzle, we only measure a single channel at a time, but brightness is a weighted average that uses 71% Green, 21% Red and 8% Blue to produce the brightness. We’re ignoring that we’re basing our calculation on 71% of the true luminance value (like a light meter would have) because it doesn’t matter. And this assumes pure green. If the green screen is paint-based, it’s polluted with Red and Blue, and suddenly, reading just the Green channel IS accurate after all, because now it’s a proxy for the other channels. Confused yet? And a light meter isn’t exempt from problems with weighted average calculations.
What matters is simply that we learn what 1 Band on Mid or 1 Band on Hi means in terms of the quality of the key. In time, we might learn that we still find the results acceptable if we stay MOSTLY within 1 band on Mid, but dip into a neighboring band once in a while.
This is a much easier, and ultimately much more reliable way to think about green screen.
Hollywood’s History of Faking It | The Evolution of Greenscreen Compositing
Go inside the history of the traveling mattes (now called chromakey) and learn the history of visual trickery used by filmmakers from the earliest filmmakers through to the modern day. Courtesy of Filmmaking IQ.
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