Name: ビデオはどのようにして発明されたのか？ (How Was Video Invented?)
Uploaded: 2021-01-14T10:25:36.000Z
Duration: 13 min 13 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

程度の副詞

Film is a very straightforward technology.

It just involves taking a two-dimensional image,

and focusing it on to a two-dimensional piece of film, and there you have a photo.

But video, and by that, I mean moving electronic images,

has a very different history with a lot of changes that have really transformed the way it works.

which is kind of fitting because that's where I get a lot of my gear to make these videos.

So I'll tell you more about them later, but now it's off to San Francisco.

I'm going to meet with a guy who knows a lot about old video gear and he's got some he's gonna show me.

- Nice to meet you Derek. Come on in. Welcome to LabGuy's World.

- [Laughs.] That's a cool spot you got here.

- The fundamental problem of video is taking this two-dimensional light image

and turning it into a one-dimensional electrical signal.

Well, the solution actually comes from the first ever fax machine,

which believe it or not, was invented in 1843 by Alexander Bain.

His invention involved a transmitter and receiver which each had a pendulum,

So what would happen is, at the transmitter, there would be a metal sheet

on which something was written or drawn using a non-conducting ink.

an electric finger, would stroke over the paper and wherever there was iron, it would conduct,

and that conducting signal was sent to the other end,

which was applied to paper with a chemical that would turn dark when electricity flowed through it,

and it would reproduce a very accurate image of the handwritten note you just made.

- Now Alexander Bain only ever transmitted static images,

but some people have called him the real father of television,

This idea of moving back and forth across an image,

But if you really want to get moving images,

well, you need to be able to scan much faster.

So we have to jump forward to 1884, and a 23-year-old German University student named Paul Nipkow.

He patented what is called the Nipkow disk,

which is basically a big disc with a spiral of holes in it.

and if I go fast enough you can see the scanning.

- You would put a light behind this Nipkow disk

and so you'd have a spot of light which scans across your subject, say a person.

And then there would be a reflected light off that person which would be picked up by some light sensors.

That would create an electrical signal which you could transmit over distance to a receiver.

Now at the receiver you use that electrical signal to modulate the brightness of a light source,

and then in front of that you place a synchronized Nipkow disk,

and so the result is a recreation of the image from the transmitter.

- So it was just barely at the limits of the ability to make a viewable picture,

and it was actually broadcast for a couple of years in Britain,

and in America and other countries did experimental broadcasts using this technique.

- This is arguably the first-ever broadcast television image.

It was broadcast for a few hours a day for several years,

and it was used by engineers to perform experiments and try to improve the quality of the broadcast.

- What it proved was that this wasn't the way to do it. [Laughs.]

- So by 1939 mechanical TV was all but phased out,

So this is a glass vacuum tube with an electron gun at the back.

And the electron gun would fire a beam of electrons at the screen,

where it was coated in a chemical which produced light when it got hit by the electrons that's called a phosphor.

And using magnetic fields, this beam was scanned across the screen

and you would vary the brightness of the beam by varying the voltage on a control electrode,

essentially determining how many electrons would get sent out in that beam at any instant to hit the screen.

So, if you send out a lot of electrons you get a bright spot,

and in that way you can produce a nice black-and-white image.

well, there were a number of dead ends along the path

to the red-green-blue pixel system that became the standard.

Like this TV with a spinning color wheel.

- I named the project Goldmark I in honor of Dr. Goldmark.

The television part is a standard black-and-white picture tube.

- It displayed 24 frames per second but each frame required six scans: blue-green-red, blue-green-red.

It worked really well, but it wasn't backwards compatible with black-and-white TVs.

so named for its three cathode ray tubes, one for each color.

And their images were combined with prisms.

is that for every inch you add diagonally to your screen

the volume of the cabinet increases by like the power of something like three and a half.

- So the ultimate solution was to have red, green, and blue phosphors for each pixel,

and three electron guns to determine their relative brightness.

- Now, the number of lines those electron beams make across the screen is, in theory,

But this is achieved by scanning every other line each sixtieth of a second,

so it actually takes two scans to make one frame.

And what you'll notice watching this is that most of the time you're actually staring at a blank screen.

The illusion of a continuous moving image is made possible by our persistence of vision,

that is, we don't stop seeing something instantaneously after light stops entering our eyes.

- So, initially I was thinking this wouldn't be too hard to film

I mean, a thirtieth of a second or a sixtieth of a second, that's not terribly fast.

But then if you think about it, 262 and 1/2 lines being drawn every sixtieth of a second,

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ビデオはどのようにして発明されたのか？ (How Was Video Invented?)

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