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Why Are Green Screens Green?

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There’s a scene in the Netflix sitcom Master of None where Aziz Ansari’s hapless commercial and B-movie actor Dev stands in front of a vast green backdrop in a film studio. “Honestly, most of this is going to be done in post [production],” the bored director of a hackneyed sci-fi film tells him. “It’s kind of meaningless. We really don’t even need you here. It’s going to be 99 percent CGI.”

The satire may have hit close to home for actors involved in Game of Thrones, the Marvel universe movies, or the countless other productions, both lavish and low-budget, that rely on a technique called chroma key for visual effects and fantastic scenery. Some actors spend hours in front of green backdrops, imagining the alien hoard, billowing fireball, or towering castle that special effects pros will later add digitally. “You kind of forget the plot a little,” said Idris Elba of working in front of a green screen on Thor, adding, “It’s a bit of, ‘Wait, what is this again? Oh, right, Frost Giant. Okay.'"

Out of all the colors on the spectrum, why green? Why does that particular hue work best for leaving a blank into which special effects can be painted?

The truth is, it doesn’t. Chroma-keying is the process of isolating a single color or brightness value in an electronic image and then making that value transparent in post-production, allowing another image or footage to be placed “beneath” the color that’s been blanked out. Although green is used so often that “green screen” and “chroma key” have become almost interchangeable, any color will work. Green is the go-to because it doesn’t match any natural skin tone or hair color, meaning no part of an actor will be edited out through chroma key.

When a green costume or prop is essential, a blue screen is often substituted. This caused a complication for the 2002 Spider-Man movie. Filmmakers had to use a blue screen for effects shots of the Green Goblin. But blue is an integral part of the web-slinger’s color scheme, so they switched to green screens for shots of the hero. Additional tricks and special effects were used to get the two characters in the same effects shot. Makers of the Justice League movie, which will inevitably feature Superman and Green Lantern side by side, take note.

While the technology might seem complex, Hollywood has been using chroma key since 1940’s The Thief of Baghdad, and local newscasts utilize it to put a meteorologist in front of a graphics outlining the forecast. This is one reason why weathermen (and weatherwomen) need to be mindful of what tie or dress they wear.

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Big Questions
Why Does Turkey Make You Tired?
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Why do people have such a hard time staying awake after Thanksgiving dinner? Most people blame tryptophan, but that's not really the main culprit. And what is tryptophan, anyway?

Tryptophan is an amino acid that the body uses in the processes of making vitamin B3 and serotonin, a neurotransmitter that helps regulate sleep. It can't be produced by our bodies, so we need to get it through our diet. From which foods, exactly? Turkey, of course, but also other meats, chocolate, bananas, mangoes, dairy products, eggs, chickpeas, peanuts, and a slew of other foods. Some of these foods, like cheddar cheese, have more tryptophan per gram than turkey. Tryptophan doesn't have much of an impact unless it's taken on an empty stomach and in an amount larger than what we're getting from our drumstick. So why does turkey get the rap as a one-way ticket to a nap?

The urge to snooze is more the fault of the average Thanksgiving meal and all the food and booze that go with it. Here are a few things that play into the nap factor:

Fats: That turkey skin is delicious, but fats take a lot of energy to digest, so the body redirects blood to the digestive system. Reduced blood flow in the rest of the body means reduced energy.

Alcohol: What Homer Simpson called the cause of—and solution to—all of life's problems is also a central nervous system depressant.

Overeating: Same deal as fats. It takes a lot of energy to digest a big feast (the average Thanksgiving meal contains 3000 calories and 229 grams of fat), so blood is sent to the digestive process system, leaving the brain a little tired.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
How Are Balloons Chosen for the Macy's Thanksgiving Day Parade?
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The balloons for this year's Macy’s Thanksgiving Day Parade range from the classics like Charlie Brown to more modern characters who have debuted in the past few years, including The Elf On The Shelf. New to the parade this year are Olaf from Disney's Frozen and Chase from Paw Patrol. But how does the retail giant choose which characters will appear in the lineup?

Balloon characters are chosen in different ways. For example, in 2011, Macy’s requested B. Boy after parade organizers saw the Tim Burton retrospective at the Museum of Modern Art. (The company had been adding a series of art balloons to the parade lineup since 2005, which it called the Blue Sky Gallery.) When it comes to commercial balloons, though, it appears to be all about the Benjamins.

First-time balloons cost at least $190,000—this covers admission into the parade and the cost of balloon construction. After the initial year, companies can expect to pay Macy’s about $90,000 to get a character into the parade lineup. If you consider that the balloons are out for only an hour or so, that’s about $1500 a minute.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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