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cover of episode How do green screens work?

How do green screens work?

2025/2/12
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Moment of Um

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Jeremy Royce
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Pop Hopkins
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Pop Hopkins: 作为Pop's One Stop Prop Shop的店主,我主要制作和销售电影电视中使用的各种道具。从太空激光枪到沙发,再到闹鬼的娃娃和普通的叉子,几乎没有我做不出来的。自从我入行以来,电影技术已经发生了巨大的变化。过去,所有的电影特效都需要自己动手制作,比如想要一个巨型 trolls,就得先做一个黏土模型,然后在微缩版的电影场景中拍摄。或者找一个身材高大的人,给他化上浓妆,穿上毛茸茸的内裤。但现在,有了电脑和绿幕技术,我们就可以创造出整个虚构的世界和生物,而不需要用到一丁点的胶水或毛茸茸的内裤。虽然绿幕技术很强大,但人们仍然需要道具。 Jeremy Royce: 我是一名电影摄影师,同时也是南加州大学的电影制作教授。绿幕技术主要用于在拍摄场景后方添加虚假背景。具体来说,绿幕是一块巨大的布料,通常悬挂在舞台的后方。相机通过捕捉红、绿、蓝三种颜色来记录世界。如果背景是单一的绿色,我们就可以完全移除它,并替换成任何我们想要的内容。我们经常会拍摄一些在现实世界中无法实现的壮观场景,比如模拟外太空环境,或者展示火山爆发的景象。在这种情况下,我们会搭建一个看起来像拍摄地点的场景,然后通过后期制作,用虚假环境替换掉绿幕。除了绿幕,我们有时也会使用蓝幕,原理是相同的。使用绿幕或蓝幕时,最重要的一点是,拍摄对象不能包含与背景颜色相同的颜色,否则在替换背景时,这些物体也会消失。后期制作软件可以移除绿幕,并用其他图像进行合成。

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From the brains behind Brains On, this is the Moment of Um. Moment of Um comes to you from APM Studios. I'm Pop Hopkins, owner and proprietor of Pop's one-stop prop shop. Um...

In case you don't know, props are all the stuff you see in movies and TV. Space lasers, couches, haunted dolls, forks, you name it. And here at Pop's One Stop Prop Shop, we make and sell the best movie and TV props you ever saw.

Do you need a bookshelf that opens into a secret hideaway? I can make that. How about a perfect replica of the Hope Diamond? But made out of glass. I can make that! A hair dryer and pepper grinder super glued together and painted to look like a shrink ray shooter? Oh yeah, no problem. I can make that.

And I'll tell you what, film technology has come a long way since I started in the biz. Used to be you had to make all your movie special effects yourself. You want a giant troll in your movie? You build a clay model and film it on a tiny version of the movie set. Or you get the biggest guy you can and stick him in a lot of makeup and some furry underpants. But now?

Holy schlamoly! With computers and something called a green screen, you can build whole imaginary worlds and creatures without even a single ounce of super glue or furry underpants. How do they do it? And how does a green screen work anyway? What's the big deal about a screen being green? Owen and Connor were wondering the same thing. Let's ask one of these whippersnapper whiz kid filmmakers all about it.

Green screens are used to basically add a fake background behind whatever the scene is that you're filming on set. Hi, hello, my name is Jeremy Royce. I'm a cinematographer and a professor of film production at the University of Southern California. A green screen is a big sheet of fabric that is usually hung at the back of the stage. So the way a green screen works is the camera

records the world by capturing three separate colors inside. It captures red, green, and blue. So if you're shooting and the background is all one color, in this case green,

you can remove it entirely and replace it with whatever you want to replace it with. We often try to film really spectacular moments that might not be possible in the real world. Maybe we're simulating what it's like to be in outer space, or we're trying to show a volcano exploding, but obviously we can't film at the base of a volcano or in outer space.

So we would go ahead and construct a set that looks like where it should be close to the camera, but then everything in the distance is going to be added in post-production after we've already filmed by replacing the green screen with that fake environment.

So in addition to green screen, sometimes we use blue screens and it does the same thing. The only rule we have is you can't have anything in the shot that's the same color as the background. Otherwise, it's going to disappear when you replace it. So if there's a scene with a lot of plants in it, we

We might use a blue screen instead of a green screen because the plants would disappear if we ended up using the green screen. The green screen can be removed through any sort of post-production software. Even basic editing software can do it. Professionally, people use a higher special effects software. It's called compositing. Compositing is when you remove the green and replace it with something else, creating a composite image of two images combined together. Um, uh,

Video cameras capture three different colors of light: red, green, and blue. But if you want, you can use computer software to digitally snip out anything on the screen that is one of those main colors. So, if you have big pieces of green fabric behind your actors, you can go back with your nifty software and tell the computer, "Hey, take out all the green and put in this digital picture of a dinosaur instead."

The computer does the work and boom! Those actors are being chased by a massive T-Rex! Fortunately for old Pop, green screens and computers can't do everything. People still need props. Which reminds me, I gotta go fill an order for five crates of realistic wax bananas. That's right, Pop's keeping busy. ♪

If you like this episode, take a second to subscribe to Moment of Um wherever you listen to podcasts. And if you want to send your brain on an adventure, well, check out the Brains On podcast where we have a whole episode all about whether you could walk all the way around the world. Want to see our shows come to life? Head to YouTube where we've got awesome animated Brains On episodes.

Search Brains On Universe on YouTube and subscribe. If you have a question, we'd love to help you answer it. Drop us a line by going to brainson.org slash contact. See you next time and the next day and every weekday. Until then, um...

Has anyone seen my banana wax?