November 23, 2023 • 46 mins
Where did green screen technology come from? How does it work? From the dawn of cinema to the latest Zoom meeting, we take a look at the tech that lets us combine different images into a single film or video.
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Speaker 1 (00:04):
Welcome to tech Stuff, a production from iHeartRadio. Hey Thearon,
Welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm
an executive producer with iHeart Podcasts. And how the tech
are you well? Here in the United States, we are
celebrating Thanksgiving, which means our office is closed, so I
(00:26):
do not have a brand new episode for you, but
I do have a pretty cool episode that we published
on June one, twenty twenty. It is titled tech Stuff
in front of a Green Screen. So I hope you enjoy.
And for those of you who are celebrating, Happy Thanksgiving,
and for those of y'all not in the United States,
(00:46):
maybe in Canada where you had Thanksgiving already. To you,
I say happy Thursday, enjoy this rerun episode of tech Stuff.
Today's topic goes by many names like chroma key, or
blue screen or green screen. The inventor of this technology
(01:09):
developed it for film, and that pun was unintentional, you know,
developed for film, but I'm gonna run with it. Today
we use this technology in film, in television, on Twitch streams,
and zoom calls, I mean all over the place. And
in the old days you weren't likely to encounter a
(01:30):
green screen unless you were inside a movie studio, like
inside a soundstage. But today there are a lot of
folks who have a green screen just stashed in their
home office. So today I want to cover this technology,
it's history and development and how it works. Now, before
I get into the history, which, as I'm sure most
(01:51):
of you know, is my modus oparandi, let's give a
quick overview of what this technology actually does. So it's
a system that allows a creator to insert images, typically
a background that's your standard use of this, and you
do it into a shot that otherwise isn't actually in
(02:13):
that location, so it could be a static image, or
the new image might be in motion itself, so it
might be video or film. This technology allows creators to
shoot in locations they might otherwise have trouble getting to,
like the bottom of the ocean or an outer space,
or in my old college dorm room because I was
notorious for locking myself out. So when you do it well,
(02:35):
it really enhances a scene. But when done poorly, it's
incredibly distracting because it's so obvious that the people or
you know whatever that are in the foreground of the
shot aren't actually in whatever the environment is. But that's
the basic idea. It's to create a composite, a combination
of multiple shots into a single new shot, so that
(02:59):
the component and it's from those two separate shots are
combined as if they're in the same place at the
same time. That's the basic idea. Now let's get to
the history, you know, the part that everyone really came
here for. But before we even get into the development
of it, we need to think about the early days
of film and talk about what film really is, because
(03:22):
that's going to help us understand the evolution of the
art form that made chroma key even a possibility. When
I say film in this case, I'm specifically referencing images
shot on a long strip of plastic upon which there
is a coating of light sensitive chemicals. Actually, there are
several layers of light sensitive particles in that thin strip
(03:44):
of film. You know, with modern film you might be
talking about twenty or more layers on that thin little
piece of plastic. These layers include binding agents, you know,
essentially gelatine and grains of silver halid crystals, which react
to the light. These are those photosensitive chemicals and also
some special molecules that bind with silver haylid crystal so
(04:06):
that they transfer energy from specific wavelengths of light, which
we perceive as different colors. When light hits the silver
haylight crystals coating this plastic, there is a chemical reaction,
and you can think of it as a chemical record
of that instant of time. Whatever light hit the film
(04:27):
is recorded there on this piece of plastic. So if
you position the lenses so that you can direct specific
light to that film, you can take a photograph. You
must use some form of shutter to block out the
light until you are ready to take your image. Then
you open the shutter. This exposes that piece of film
(04:47):
to the light that's being reflected off of whatever it
is you're photographing. Remember when we see things, we're seeing
light bouncing off of that and the color of the
stuff we see is dependent upon and which frequencies of
light bounce off of that thing. So then the shutter
closes on your camera and you've got your chemical record.
(05:09):
And the shutter is necessary because, as I said, these
chemicals react to light. If you just had this stuff
exposed to light all the time, it would have already reacted.
You would not be able to use it to take
a photograph of anything if you want to learn more
about this process, which is fascinating, but really the process
of photography is far enough out of the scope of
(05:30):
this episode that I don't want to go into it
much further. I do recommend you go to HowStuffWorks dot com.
That's my old employer. I don't technically work for How
Stuff Works anymore, but you can go to that website
and you look up the article how Photographic Film Works.
It was written by Chuck Woodworth and it's a great
(05:50):
example of the how Stuffworks style, and it goes into
the chemistry and physics of the photographic process, but we'll
skim over the rest of that for the purpose of
this episode. So now the film on the camera has
a latent image on it, and it represents the moment
in time the shutter allowed light to pass from the
(06:10):
lens to hit the film. But in a film camera,
a cinema camera, you're talking about a series of latent images.
Motors pull this strip of film at a steady speed
through the frame of the camera, where the shutter opens
and closes at a regular frequency, and the standard speed
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of capturing images is twenty four frames per second. So
a film camera is capturing twenty four photographs every second.
The latent images need some processing in order to create
something that can be fed through a film projector. The
development process creates a negative image of the chemical record,
and that means that the darkest areas of the image
(06:55):
represent the spots where the film received the most light.
It's the opposite of what you would expect, right. Anything
that would be dark in a photograph will be light
on a negative and vice versa. This negative has to
be transferred onto another role of film to create a
positive image in a process that I'm also not going
to cover because we need some time for actual topic. Right.
(07:16):
So when we watch a film, we have the perception
that what we're viewing are moving objects up on a screen,
but that is an illusion. What we're really seeing with
true film is that it's a series of photographs. The
projector is playing those photographs at the same speed that
the film camera used to make them twenty four frames
(07:36):
per second usually. I mean, if you want to play
stuff in slow motion, then you would shoot a film
at a much higher frame rate, like forty eight frames
per second, but you would play it back at the
standard twenty four frames per second, and that would give
you the slow motion effect. And back in the old days,
cameras were hand cranked, so you would get kind end
(08:00):
of twenty four frames per second, but this would result
in sort of that hurky jerky movement we associate with
old movies that was hand cranked cinematography, and sometimes people
would turn the crank a little faster or a little
slower than others, so you don't really have a consistent
experience there, because the playback speed, especially if you're playing
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it in a modern projector, is going to be standard,
even if the recording speed wasn't. But never mind all that.
If you were to stop the projector's reels at any
given moment in the playback of a film, you would
see a still image. You would advance the reel by
one frame, and you would see the next image, the
next photograph in that series, and you would likely be
(08:44):
able to pick out how things are slightly different from
the first frame you looked at and the next frame.
And this is the same principle that's behind animation. If
you've ever taken a pad of sticky notes and you
drawn little figures on page after page after page that
when you flip the pages, you get a simple little cartoon,
then you've engaged in the same art form as great cinematographers.
(09:06):
Then maybe your work was even better than theirs. I'm
not one to judge. Now, why would I go to
the trouble to cover the basics of film? Well, it's
because the very nature of film inspired certain people to
experiment with it, to try stuff that would be impossible
to replicate in a real world setting, or at least
it would be really difficult. Film wasn't a substitution for
(09:27):
a theater. In theater, you can create a few interesting effects.
Generally your options are limited to things like lighting tricks,
maybe some creative sets or costumes, maybe an even a
stage illusion or two, and perhaps some sound design. But
with film there were other possibilities, and one fellow who
recognized those possibilities was the French filmmaker and illusionist George Mellier.
(09:53):
He was born in Paris, You know Paris in eighteen
sixty one. Let that sink in for a moment. This
man was born while the Civil War was going on
in the United States. He became interested in stagecraft and magic,
and by the eighteen nineties he was a successful stage magician.
In eighteen ninety five, he saw an early film exhibition
(10:14):
made by the Lumier Brothers and he became entranced by
this new medium. His experience and illusions encouraged him to
find ways to experiment with film to achieve new effects,
stuff that wouldn't be possible to do in the real world.
He was a special effects and film pioneer. He established
methods to shoot slow motion, stop motion animation, to do dissolves,
(10:37):
and tricks like superimposition and double exposure. Around eighteen ninety eight,
Melier had a really cool idea. He wanted to create
a truly bizarre special effect in which an actor would
appear to remove his own head on screen. But how
would he accomplish this? While the secret was in shooting
multiple exposures of the same real film. Typically, after you
(11:01):
expose film to light, you want to avoid doing that
again because you will interfere with that chemical record. You know,
if you were to ever take photographs with a film
camera and then someone were to open up the back
of the camera and expose the film to regular light,
you could potentially ruin shots that were already made, plus
(11:21):
ruin the film for the next couple of shots. It's
not something that you typically want to do. More light
will cause further reactions, chemical reactions on the actual plastic film,
and your shot gets ruined. If you've ever used the
cameras that don't quite line up the film properly at
the very beginning or the very end, you might even
notice that a couple of photos on those sections of
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the film role have two sets of images super imposed
on top of one another, and that's because that little
section of film was exposed more than once. Melia did
this on purpose. He would set up a shot and
he would use a lens that had some of the
lens blacked out so that light could not pass through
(12:06):
that part of the lens. And we refer to this
as a mat matte, and you can think of it
like a mask for the lens, and that would mean
a section of each frame corresponding to that part of
the mat would remain unexposed to light. He would shoot
the scene as rehearsed. Afterward, he would rewind the exposed
film in the camera, beat it right back in as
(12:27):
if he was going to shoot something all for the
first time, and he would then replace this mat with
a new one and the new mat would block out
everything except the section that previously was unexposed. So in
other words, the part that was black would now be clear,
and the rest of the lens that was previously unblacked
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would be blacked. So you replace one mat with a
different one. So he would then be able to film
something totally new into this same role of film, and
this time the would pick up a new scene and
by changing things between one section and the other, he
could create weird effects like the head removal trick. It
would appear as though all of this was shot at
the same time on the same role of film, but
(13:13):
in fact, through careful control of where the light would go,
Melia would use the same film twice or more to
produce cool results. And if you want to see an
example of what I'm talking about, and I highly recommend
you check this out because it is amazing even today,
go to YouTube and do a search for the short
film four Heads Are Better than One. The creativity of
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this film, which by the way, lasts less than a minute,
is still astonishing. To say his experimental work was influential
would be a gross understatement. Other filmmakers, inspired by the
work of Melia tried new techniques that built upon the
foundation he established. For example, filmmaker and documentarian Norman Dawn
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wanted to show films at historic buildings around California, but
several of those buildings had been damaged or even partly destroyed.
Other historic buildings had modern stuff like light poles in
front of them. He didn't want that to be in
the shot, so he wanted to show the buildings as
they had appeared in their original form before the decay,
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before modern technology had advanced into the area. So he
came up with a really clever idea. Dawn placed a
pane of glass between the camera and the scene he
wanted to shoot, and on that pane of glass he
had paintings to enhance the scene. If a building's roof
had caved in, he would frame up the shot and
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then have an artist paint a roof on the glass
so that when viewed through the camera, the painting and
the building behind it would line up and the building
would appear to be whole again. Or he might want
to cover up stuff like those telephone poles. He would
have an artist paint trees on the so from the
camera's perspective the polls were hidden. His process also involved
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double exposures. This was an example of a Matt painting,
and he would claim credit for inventing this, and he
even applied for a patent on it. But subsequent lawsuits
established that other filmmakers were using similar approaches, and the
patent office ultimately denied the claim, but Matt paintings would
become an important part of filmmaking from that point forward.
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One disadvantage to these early film effects was they required
the camera to remain stationary through the whole process. You
couldn't move the camera at all, or else your shots
wouldn't line up, so you wanted the camera to remain
in one place through all of these different exposures. Another
problem was that no action could cross the Matt line
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because it would get cut off as it moved beyond
that invisible at least from the audience's perspective line. Now,
let's move on up to nineteen eighteen, when a guy
named Frank Williams created the Williams process, which honestly seems
pretty convenient to me. The Williams process allowed for more
(16:07):
movement and involved shooting actors against a solid background such
as a black or blue curtain on very high contrast film.
The process sometimes required multiple transfers onto new film until
you arrived at a black silhouette against a pure white background,
the negative image of what you were shooting before, and
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this was called a holdout matt. The way these transfers
typically would work is that you would put one strip
of shot developed film into a camera, so you've already
shot on it, but you're putting it through the camera again.
And you would put a second strip of film that
is unshot, it's unprocessed, no lights hit it, and put
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it right up against the first developed piece of film.
You would shine light through the camera and you would
let it just run. And this way you would transfer
for the images from one strip to the other. And
this was called bypacking because you were putting two different
pieces of film through the camera to achieve this process.
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And you could also do this not just with developed
film where you're making copies. You could do it with negatives.
You could do it in a way to increase contrast
from copy to copy until you were able to create
a holdout mat reverse printing. The holdout matt creates a
white silhouette on a black background or a cover mat.
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So now you've got a holdout matt and a cover mat.
You would take the footage of a previously shot background.
Let's say it's a foreboding forest, so you've shot your
actors in a sound stage, but you want the background
to be this really scary looking forest, and you would
bypack a film camera with the background footage that you
had shot and the black silhouette holdout matt of the
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actor's footage that you shot. Then you would transfer this
combination to a third piece of unexposed film by again
shining a light through those other two pieces. And because
the background on the holdout mat is white, the light
passes through it easily and it hits the previously shot
background image that comes through and gets copied onto the
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blank film. The silhouette of your actors is black that
prevents light from passing through. So the previously blank third
piece of film now has a background image and this
dark silhouette of actors moving through the frame. Then you
would have to take that piece of film that has
this black silhouette and you have to bypack it with
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the original footage of the actor, not the silhouette, but
the actual actor footage. And now the real actor is
on top of the silhouette and appears to actually be
in front of whatever the background image is, in our case,
the foreboding forest. Because this type of matt moves from
frame to frame, it's called a traveling mat. And if
you remember Fraggle Rock you might remember Traveling Matt is
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the name of Gobo's uncle. Gobo, by the way, is
another stage and lighting term. It stands for a template
or stencil that controls the shape of a lamps emitted light.
So some of the Fraggles had fun industry names, Gobo
and traveling Matt. When we come back, we will continue
down the history of how chroma key came about. But
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first let's take a quick break. Before the break, I
was talking about the Williams process, but C. Dodge Dunning
would improve upon the Williams process by using yellow light
to shoot the actor in front of a blue screen,
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creating the Dunning process, and this was used extensively in
the classic nineteen thirty three film King Kong, and they
weren't great for black and white film. Remember this is
before anyone was shooting on color. So although I mean
there were ways of treating film to create color, but
this was standard black and white film, so you didn't
have to worry about the weird lighting. But if you
(20:10):
wanted to shoot in color, that was going to cause
or require other considerations. Around the same time, engineers were
developing the optical printer, which really simplified the process of
transferring images from one strip of film to another. Now
I talked about bypacking, but the optical process could be
(20:31):
an alternative to that. It didn't eliminate it, but it
was a different way to achieve the same thing. Essentially,
an optical printer has a projector on one side and
a camera on the other. The projector shoots out a
projected image that then gets copied onto a new, unexposed
role of film inside the camera. And it also allowed
filmmakers to create new effects by changing the focal point
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of the camera or the distance between the projector and
the camera. And rather than bypacking camera, you just use
this process you could get better results. The first mass
produced optical printer hit the market in the mid nineteen forties.
It came from a company called Acme Donne. In addition,
filmmakers created rear projection backgrounds, so in these actors would
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perform in front of a screen like a projection screen,
not a green screen or a blue screen, and behind
that screen would be a film projector and it would
provide a projected background image. You could do this in
place of the processes have already described, putting your actors
in front of a screen that shows whatever background you wanted.
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The background could be fairly static, but didn't have to be.
You could include a background that was actually dynamic, showing movement.
It could be a film in of itself. This was
used a lot in shots where people were in vehicles
and talking with one another. So rather than setting up
a car on a trailer and shooting it in the
real world with the camera on the trailer, or worse yet,
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trying to figure out how to fit a camera onto
a real moving car that's operated by an actor, you
would typically have performers sitting in a stationary vehicle and
the screen behind and sometimes to either side of them
would display previously shot footage of scenery going by from
the correct perspective, as if the car were driving down
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the road. This wasn't necessarily convincing, mind you, but it
was an interesting technique. In nineteen thirty two, engineers created
a process to produce films in color called appropriately Technicolor. Interestingly,
in this process, images would be captured to three strips
of black and white film at this stage as the
(22:40):
tri strip approach. This was not the original version of Technicolor.
It was technically the fourth incarnation of the Technicolor technology,
but it's the important one for our discussion. So how
do you produce a color image if you're using black
and white film as your medium? Well, first you have
to shoot your footage. And inside an early Technicolor tri
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strip camera behind the lens was an optical cube and
it acted as a prism. Prisms break up incoming light
into bands of frequencies, and you've likely had one, or
played with one, or at least seen one. That's the
kind of stuff, you know. A light goes through it
and then it makes rainbows. You see a little rainbow
pattern projected somewhere. This prism would break up the incoming
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light into three general bands that corresponded with red, green,
and blue. Each of those bands of light would hit
one of three strips of black and white film inside
the camera, so one strip of film would be exposed
to all the red light coming from a scene, one
from all the green light coming from a scene and
one from the blue. The concentration of each color in
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the scene would affect how much light was hitting each
strip of film, So you'd end up with three negatives
of your scene that were all perfectly synchronized, all of
them in black and white, but each with different levels
of brightness for different objects. It all depended on what
color the objects were in the scene. A red chair,
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for example, would appear as a very prominent image on
the black and white film that was hit with the
red light, while it would be less noticeable in the
green and blue strips. Now you would develop the negatives,
and you would process the film, the three strips of film,
and you would print them just as you would a
regular black and white movie, and you would technically have
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three identical black and white sequences that only well, not
identical because the brightness would be different between each, but
they would be of the exact same shot. You would
then process these film strips by dying each of them
in their respective color, so you would literally end up
with a red tinted strip of film, blue tinted strip
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of film, and a green tinted strip of film. Then
you would take these three died strips of film, and
you would laminate them together and you would print that
to a new role of film and you would have
a color motion picture which was fairly accurate, although the
technical process would evolve over time to become even more so.
(25:16):
And the Technicolor process is really what set the stage
for the next part of our story. It's why I
felt the need to even explain how it worked. Now
we get to a guy named Lawrence Larry Butler. He
was born in nineteen oh eight and he was actually
a second generation optical effects professional. His father, William Butler,
had been a silent film actor who frequently appeared in d. W.
(25:39):
Griffith films. Larry worked on several motion pictures in the
nineteen thirties before creating a new compositing process in nineteen
forty for the film The Thief of Baghdad. In that film,
Butler introduced a new special effect approach and this would
be the birth of the blue screen. All right, So
let's break down this process, and it builds on Technicolor
(26:01):
as I mentioned. So with Technicolor, you get three prints
of your shot, right, one for red, one for green,
one for blue. If you created a solid backdrop in
one of those three colors and shot something in front
of that background. You could use that particular strip of
film to create a traveling mat. Remember, the color would
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show up as very bright in your black and white
film print because a lot of light is reflecting off
of that particular color. Effectively, you could make a negative
image of whatever the foreground was. The stuff you're shooting
would be dark and the background would be bright. You
would have to make sure that nothing in the scene
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had the same color, however, or else your traveling matt
would effectively have holes in it because the color of
the foreground would match the color of the background. You've
probably seen this if someone's ever worn a shirt that's
the same color as whatever screen they're supposed to be
standing in front of. The same thing would even happen
in film. It's just that it would happen well in
(27:05):
advance of anyone being able to see it happen, like
see the effect of it. Because you had to do
all this other processing. The other two strips of black
and white film would have pretty dark backgrounds because the
light projected onto them wouldn't match the color of the backdrop. Right,
And you could take the film of a background shot.
This is called the background plate. So this is previously
(27:26):
shot film of whatever it is, whatever setting you're planning
on putting this stuff, and then you use the traveling
mat against it in an optical printer, and that would
produce a silhouette of the foreground action. And it's that
black hole that's the shape of whatever it was you
were shooting. And you would take this new print in
which you've got the silhouette of your action, it's the
(27:46):
previously filmed backdrop, and combine that with the processed color
film to fill in that hole left by the traveling mat.
So you've got this possibility now of creating a traveling
mat by taking advantage of the technicolor process. But then
you have to make a decision which of the three
colors should be the focus. Whichever color you choose is
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going to determine what you can shoot, because you can't
have any objects or people in the scene that have
that color on them, or the traveling matt won't work properly.
This is what I mean when I say, if you've
ever seen someone on screen who's had a background effect
bleed onto them because the color of clothing they're wearing,
what was letting it happen. You've seen that issue. So
(28:30):
Butler decided to go with blue as the backdrop color,
largely because he determined it was a color far removed
from skin tones, and he wanted to make sure that
actors wouldn't match the color of the background and mess
everything up. So as long as you weren't shooting anything
blue in the foreground, you could use this process to
make a composite image of the foreground action against a
(28:51):
different background. He also would combine the blue negative image
with the green positive or processed image to create a
better tracking matt, something a more solid silhouette. In other words,
Butler's contribution led to him winning an Academy Award for
this process. Still, this was an incredibly time consuming approach.
(29:12):
I'm sure you gathered that just from my explanation of it.
Because you had to shoot your sequence, you had to
create the traveling matte negative, you had to combine that
against the background footage, and you had to combine that
combination of the background image and the traveling matt with
the fully processed color image and then ultimately come up
with a composite piece of film. It gave filmmakers way
(29:37):
more options when making movies. It allowed them to shoot
stuff inside a sound stage rather than whatever location they
would have to go to, and it even opened up
locations that would otherwise be impossible. But it did require
a lot of post production time and work. It also
required a close attention to lighting, otherwise you would end
up with blue halos around people and that was pretty
(30:00):
aren't distracting. In fact, all of these different approaches required
really good lighting, sometimes really intense lighting, so it would
also create pretty uncomfortable shooting conditions. It would get really
hot in those sound stages. So while it was phenomenal technology,
it required a lot of finesse to use it properly,
and a human touch was absolutely necessary through every stage
(30:21):
of the process. Now, over the next several years, really decades,
movies benefited from this technology. The tech allowed filmmakers to
do all sorts of neat things. Not only could they
make it seem like actors were in places that would
be hard or difficult to shoot in or places that
maybe don't even exist, they also allowed for stuff like
(30:42):
the incorporation of animation and live action in a way
that wasn't really possible. Before I'll get back to that again,
in a second. But in the early nineteen fifties, Eastman
Kodak created the color motion picture film that simplified the
process of shooting on color significant So, rather than exposing
three strips of black and white film to different bands
(31:04):
of light and then processing them to create a composite
color image, this new film actually contained all the layers
that corresponded to blue, green, and red. They each had
essentially filters and dyes in them, and each layer effectively
had its own silver halide crystals and respective dyes, and
streamlining the process for shooting on and developing color film.
(31:26):
You just had to have one strip, not the tri
strip approach of Technicolor. It really changed things. Also, by
tweaking the blue screen process, some inventors were able to
get spectacular results. This gets us back to that live
action and animation discussion. That would be Petro Vlajos, who
was the engineer who worked on a little film called
Mary Poppins in the early nineteen sixties. Vlahos wanted to
(31:49):
improve upon the technology that Butler had created, and one
of the issues he sought to address was that the
color blue used for blue screens wasn't a specific wavelength
of light. You got to remember that the wavelength of light,
or if you prefer the frequency of light, the two
are related, determines the light's color, the color that we perceive,
(32:10):
and the wavelengths corresponding to The blue screens of the
day ranged from four hundred and thirty five nanometers to
five hundred nanometers, and that meant any color blue that
fell in or near that range was off limits for
use in a scene. Vlajos figured there had to be
a better way, and he decided to use a different
backdrop color entirely yellow, but not just any yellow. He
(32:32):
wanted a precise yellow, the yellow that comes from sodium
gas discharge lamps. When you excite sodium gas, essentially when
you energize it with electricity, the gas gives off a
distinct yellow light with a wavelength of five hundred eighty
nine nanometers. As long as nothing in the camera frame
matches that precise shade of yellow, you could have all
(32:53):
sorts of colors in the shot, including different shades of yellow,
and not have to worry about skimping on things like
blue costume pieces. Paired with this was a customized camera
that contained a prism that could isolate the five hundred
and eighty nine wavelength of light. Vlahos was able to
produce an incredibly precise and accurate traveling matt this way,
(33:15):
which meant Disney could place actors on any separate background
without worrying about the effect showing at the seams. In fact,
in one sequence, Mary Poppins is wearing a hat that
has this veil like material on it, and you can
actually see the background, the anime background, through the veil,
and that's because of the precision of this approach. There
was one small hiccup, which was that Vlahos only had
(33:38):
one working prism that could isolate this specific band of light,
this five hundred and eighty nine nanometer band of light,
so they only had one sodium vapor camera as a result. Now,
when we come back, we're going to look at the
further evolution of this technology, including how it has changed
(33:58):
once the digital realm because came a reality. But first
let's take another quick break. I've stuck with the film
world for this podcast so far, but i also have
to talk about the use of chroma key technology in
(34:18):
the world of live television. See Mary Poppins came out
in nineteen sixty four, but the first use of chroma
key on live TV was in the late nineteen fifties.
This is the same technology that would become the basis
for TV weather reports, where the meteorologist stands in front
of a wall which seems to have a dynamic map
on it that can change from one image to the next.
(34:40):
But if the process I've described required so many steps,
if you had to do so much post production on
the film, how could you take that same basic idea
and make it work in the realm of television, in
real time live broadcast. Frank Gaskins and Mitt Altman led
this effort at NBC in the nineteen fifties. They created
(35:00):
a television camera approach to chroma key and tested it
out in nineteen fifty seven with a live broadcast of
Matinee Theater. The specific story they chose to serve as
the first experiment here was an adaptation of The Invisible Man,
and that was fitting because the nineteen thirty three film
adaptation of The Invisible Man had relied heavily on the
(35:22):
old Williams process. The live television version initially relied on
two cameras. One camera would capture a background image, the
other camera would be the four ground camera that would
be for all the action in the sequence, and behind
all this action would be a blue backdrop. Combining these
two sets of images simultaneously in a device called a
(35:45):
chroma key amplifier would create a live composite video. Feed.
Engineers at RCA created the actual technology, and I think
it's best if I just quote directly from the nineteen
fifty eight edition of the journal Electronic Ada that describes
this process. So here's a quote. A switching signal or
a color key used in association with the special effects amplifier,
(36:09):
controls the signals sent out over the air. The switching
signal is in turn created by the camera photographing the
live action in front of the blue screen. While the
camera is scanning the blue screen, the switching device automatically
activates the second camera, which projects the background. When the
scanning signal reaches an area covered by the live actors,
(36:31):
the switching device turns off the camera projecting the background
material and transmits the action. Now that's the end of
that quote. You could also feed images directly to the
chroma key amplifier. It didn't have to be a live
video from a second camera, so you could provide an
image like a map, allowing a meteorologist to stand in
front of it otherwise blank blue or green screen and
(36:53):
gesture at various regions. The audience at home would see
the meteorologist appearing to stand in front of the map,
or may be a summary of the forecasted whether for
the week, and not just a blue screen or a
green screen. Around the nineteen seventies, that's when we started
to see a gradual shift, particularly in television, from blue
screens to green ones. Part of that was because of
(37:16):
a very slow transition into digital technology. It would become
more important as digital cameras became a thing. Digital cameras
were better attuned to doing this with greens rather than
with blues, although you can do either. But another big
reason was just that people don't tend to wear a
lot of green, whereas blue was a pretty and still
(37:37):
is a pretty popular color. And once in a while
someone on camera would forget that they're wearing blue, and
then they'd step in front of a blue screen and
suddenly their jacket or their shirt or their tie or
whatever would become part of the background image. Back to
film for a moment, we're gonna leave TV for a second.
In nineteen eighty a guy named Richard Edlund, who worked
(37:59):
on a little film called The Umpire Strikes Back, made
another big contribution to the chroma key process Edluin developed
a quad optical printer which both sped up the process
for producing composite film shots and also brought the price
down as well. I mean, if you think about it,
saving time means saving money. He also developed a computer
(38:22):
controlled system of cameras which allowed for very precise camera movements,
and that meant you could create choreographed shots of foreground
and background and composite them together and have them match
up perfectly. It was also really effective for processing images
that were shot with miniatures, which was done a lot
in the original Star Wars series. So it was still
(38:43):
a painstaking process, but now a lot more could be
done on one piece of equipment per pass, as opposed
to having to do a process on a piece of equipment,
then do it again and then again and again until
you finally got whatever result you were after. Gradually, software
would creep into the realm of film and video effects,
(39:03):
and this leads us to a version of chroma key
that I think is actually the easiest to understand. It's
technically advanced, but the principle is simple. So let's say
that you want to do a Twitch stream and you're
playing a video game live, and you want your viewers
to see you sitting in front of the video game footage.
(39:24):
So once to make a dynamic background, a video gameplay
behind you. So you go out and you buy a
green screen and you set it up behind your gaming chair.
You throw up some lights more on that in the second,
and you launch a program that will insert your video
game capture as a custom digital background. Your viewers will
(39:45):
see you sitting in front of a screen otherwise filled
with I don't know, Skyrim or Minecraft or the untitled
Goose game or whatever it is you're playing. What's going
on on a technical level, Well, the digital world is
different from the analog world in lots of ways, but
importantly for our discussion, it comes down to how in
(40:05):
the digital world everything ultimately boils down to numeric values.
You or I could have a debate about whether a
particular color is aquamarine versus arrow blue, versus blue green
versus dark cyan, or whatever it may be. But in
the digital world, every color ultimately has a numeric value.
(40:29):
Assuming whatever we're looking at is a solid color, you
could designate that solid color with a specific numeric value
in computer software and then replicate it or immediately identify
it within any scene you might see where I'm going here.
With video software, you can designate a specific color from
one video source. This specific color is the chroma, as
(40:54):
it were, and this is the color you want to
replace or key Outdo software analyzes information that's coming from
say a digital camera feed into your computer, and it
looks for any signals that map to the value or
values of the color or colors you've picked. Most software
lets you fine tune this, so you can adjust the
(41:16):
settings to hone in on the specific shade of green
or blue or whatever it is that you plan to
key out. Anything that matches that value or range of
values then gets turned into a transparent video layer. The
secondary image in our case, the video game footage that
we're creating as we're playing this game shows through this
(41:40):
transparent layer, and you can actually think of the foreground
video as an overlay on top of the digital background
layer the video game footage. Anything transparent in that overlay
will show the background through the solid stuff presumably you,
the Twitch player will block the background image so viewers
(42:03):
will be able to see their favorite Twitch streamer sitting
in front of a video game. The software does all
the work for you, creating the composite video feed that
the viewer sees. That software, by the way, isn't Twitch itself.
Twitch is a video streaming platform, but to actually do
these sort of effects, you'd need to use some other
piece of software, such as some version of open broadcaster
(42:25):
software or OBS. And there are a lot of different
versions of video broadcasting software available for folks to play with,
from free stuff to professional grade stuff. This type of
versatility is the kind of stuff that previously you would
have had to have worked in like a TV studio
to have access to, but now anyone with a sufficiently
beefy computer can run this kind of operation. For this
(42:47):
to work well, you'd want to have really good lighting,
both for the foreground and for the background drop. You
want the lighting on the green screen you're using to
be nice and even, and you want to eliminate any
chef because if you're casting a shadow on the green screen,
the camera will pick up that part of the green
screen as being a darker color and it might even
(43:10):
be dark enough that the video software doesn't identify it
as the color that you want to key out, So
in those cases you would get these weird video artifacts
on screen. As a result, it'd be really distracting. So
ideally you want lights that illuminate the green screen evenly
and are dedicated just for that purpose. If you're lighting
yourself directly from the front, you're not using a ring
(43:32):
light or anything like that, then you're going to be
casting a shadow behind you, unless your Peter Pan, in
which case I guess you just think happy thoughts. Now,
this flies for stuff like Zoom meetings and Twitch streams,
but when it comes to professional grade film, it's not
really up to snuff. Software can do a bulk of
(43:52):
the work, but good old human effects artists are still
needed to make sure everything is coming out well. They
can step in and do some quality control, can tweak
things that can fix any issues that pop up, and
that pays off. You've probably seen a movie that had
phenomenal attention to this process and the effects are top notch,
and you've probably seen other movies where, due to whatever reason,
(44:14):
maybe it was budget, maybe it was just the talent
of the people working on it, you could tell that
such care wasn't given to the process, and it shows
in the final product. I still think films like Jurassic
Park I'm talking about the original Jurassic Park hold up
pretty darn well. And part of that is that the
movie depended on a mixture of different effects. Some of
(44:35):
them were computer generated and keyed in, some were robotic effects.
But a lot of this has to do with the
fact that the effects team as a whole took tremendous
care to produce results that were really convincing to the eye.
And that's the story behind chroma key and green or
blue screen technology. It's a super interesting approach to creating
(44:56):
a composite moving image, and frankly, there's going to be
a lot of other topics are around this that I
can go into. I could probably talk even more about
optical printers, for example, and the various approaches to film processing.
And you can see that while the actual chroma key
process is very different between film and digital video, the
(45:17):
basic idea of replacing one color or one element in
a shot with something from a totally different source remains
the same. It's the same underlying principle. No matter what
the actual process is. Yeah, yeah, this this screen bean
cast role is tight, y'all. Oh my god, mashed potatoes?
(45:40):
Who invented mashed potatoes? That give that person all the
Nobel prizes? Okay, that's it for the classic episode tech
Stuff in front of the grade screen. I hope you're
having as filling a Thanksgiving as I am. It's great,
very thankful for you, every one of you. I'm gonna
(46:02):
go take a nap, and next week we'll be back
with all new episodes. That should be very well rested
because I planned to sleep for about eighteen hours. Take care,
and I'll talk to you again really soon. Tech Stuff
(46:23):
is an iHeartRadio production. For more podcasts from iHeartRadio, visit
the iHeartRadio app, Apple Podcasts, or wherever you listen to
your favorite shows.
Welcome to tech Stuff, a production from iHeartRadio. Hey Thearon,
Welcome to tech Stuff. I'm your host, Jonathan Strickland. I'm
an executive producer with iHeart Podcasts. And how the tech
are you well? Here in the United States, we are
celebrating Thanksgiving, which means our office is closed, so I
(00:26):
do not have a brand new episode for you, but
I do have a pretty cool episode that we published
on June one, twenty twenty. It is titled tech Stuff
in front of a Green Screen. So I hope you enjoy.
And for those of you who are celebrating, Happy Thanksgiving,
and for those of y'all not in the United States,
(00:46):
maybe in Canada where you had Thanksgiving already. To you,
I say happy Thursday, enjoy this rerun episode of tech Stuff.
Today's topic goes by many names like chroma key, or
blue screen or green screen. The inventor of this technology
(01:09):
developed it for film, and that pun was unintentional, you know,
developed for film, but I'm gonna run with it. Today
we use this technology in film, in television, on Twitch streams,
and zoom calls, I mean all over the place. And
in the old days you weren't likely to encounter a
(01:30):
green screen unless you were inside a movie studio, like
inside a soundstage. But today there are a lot of
folks who have a green screen just stashed in their
home office. So today I want to cover this technology,
it's history and development and how it works. Now, before
I get into the history, which, as I'm sure most
(01:51):
of you know, is my modus oparandi, let's give a
quick overview of what this technology actually does. So it's
a system that allows a creator to insert images, typically
a background that's your standard use of this, and you
do it into a shot that otherwise isn't actually in
(02:13):
that location, so it could be a static image, or
the new image might be in motion itself, so it
might be video or film. This technology allows creators to
shoot in locations they might otherwise have trouble getting to,
like the bottom of the ocean or an outer space,
or in my old college dorm room because I was
notorious for locking myself out. So when you do it well,
(02:35):
it really enhances a scene. But when done poorly, it's
incredibly distracting because it's so obvious that the people or
you know whatever that are in the foreground of the
shot aren't actually in whatever the environment is. But that's
the basic idea. It's to create a composite, a combination
of multiple shots into a single new shot, so that
(02:59):
the component and it's from those two separate shots are
combined as if they're in the same place at the
same time. That's the basic idea. Now let's get to
the history, you know, the part that everyone really came
here for. But before we even get into the development
of it, we need to think about the early days
of film and talk about what film really is, because
(03:22):
that's going to help us understand the evolution of the
art form that made chroma key even a possibility. When
I say film in this case, I'm specifically referencing images
shot on a long strip of plastic upon which there
is a coating of light sensitive chemicals. Actually, there are
several layers of light sensitive particles in that thin strip
(03:44):
of film. You know, with modern film you might be
talking about twenty or more layers on that thin little
piece of plastic. These layers include binding agents, you know,
essentially gelatine and grains of silver halid crystals, which react
to the light. These are those photosensitive chemicals and also
some special molecules that bind with silver haylid crystal so
(04:06):
that they transfer energy from specific wavelengths of light, which
we perceive as different colors. When light hits the silver
haylight crystals coating this plastic, there is a chemical reaction,
and you can think of it as a chemical record
of that instant of time. Whatever light hit the film
(04:27):
is recorded there on this piece of plastic. So if
you position the lenses so that you can direct specific
light to that film, you can take a photograph. You
must use some form of shutter to block out the
light until you are ready to take your image. Then
you open the shutter. This exposes that piece of film
(04:47):
to the light that's being reflected off of whatever it
is you're photographing. Remember when we see things, we're seeing
light bouncing off of that and the color of the
stuff we see is dependent upon and which frequencies of
light bounce off of that thing. So then the shutter
closes on your camera and you've got your chemical record.
(05:09):
And the shutter is necessary because, as I said, these
chemicals react to light. If you just had this stuff
exposed to light all the time, it would have already reacted.
You would not be able to use it to take
a photograph of anything if you want to learn more
about this process, which is fascinating, but really the process
of photography is far enough out of the scope of
(05:30):
this episode that I don't want to go into it
much further. I do recommend you go to HowStuffWorks dot com.
That's my old employer. I don't technically work for How
Stuff Works anymore, but you can go to that website
and you look up the article how Photographic Film Works.
It was written by Chuck Woodworth and it's a great
(05:50):
example of the how Stuffworks style, and it goes into
the chemistry and physics of the photographic process, but we'll
skim over the rest of that for the purpose of
this episode. So now the film on the camera has
a latent image on it, and it represents the moment
in time the shutter allowed light to pass from the
(06:10):
lens to hit the film. But in a film camera,
a cinema camera, you're talking about a series of latent images.
Motors pull this strip of film at a steady speed
through the frame of the camera, where the shutter opens
and closes at a regular frequency, and the standard speed
(06:33):
of capturing images is twenty four frames per second. So
a film camera is capturing twenty four photographs every second.
The latent images need some processing in order to create
something that can be fed through a film projector. The
development process creates a negative image of the chemical record,
and that means that the darkest areas of the image
(06:55):
represent the spots where the film received the most light.
It's the opposite of what you would expect, right. Anything
that would be dark in a photograph will be light
on a negative and vice versa. This negative has to
be transferred onto another role of film to create a
positive image in a process that I'm also not going
to cover because we need some time for actual topic. Right.
(07:16):
So when we watch a film, we have the perception
that what we're viewing are moving objects up on a screen,
but that is an illusion. What we're really seeing with
true film is that it's a series of photographs. The
projector is playing those photographs at the same speed that
the film camera used to make them twenty four frames
(07:36):
per second usually. I mean, if you want to play
stuff in slow motion, then you would shoot a film
at a much higher frame rate, like forty eight frames
per second, but you would play it back at the
standard twenty four frames per second, and that would give
you the slow motion effect. And back in the old days,
cameras were hand cranked, so you would get kind end
(08:00):
of twenty four frames per second, but this would result
in sort of that hurky jerky movement we associate with
old movies that was hand cranked cinematography, and sometimes people
would turn the crank a little faster or a little
slower than others, so you don't really have a consistent
experience there, because the playback speed, especially if you're playing
(08:22):
it in a modern projector, is going to be standard,
even if the recording speed wasn't. But never mind all that.
If you were to stop the projector's reels at any
given moment in the playback of a film, you would
see a still image. You would advance the reel by
one frame, and you would see the next image, the
next photograph in that series, and you would likely be
(08:44):
able to pick out how things are slightly different from
the first frame you looked at and the next frame.
And this is the same principle that's behind animation. If
you've ever taken a pad of sticky notes and you
drawn little figures on page after page after page that
when you flip the pages, you get a simple little cartoon,
then you've engaged in the same art form as great cinematographers.
(09:06):
Then maybe your work was even better than theirs. I'm
not one to judge. Now, why would I go to
the trouble to cover the basics of film? Well, it's
because the very nature of film inspired certain people to
experiment with it, to try stuff that would be impossible
to replicate in a real world setting, or at least
it would be really difficult. Film wasn't a substitution for
(09:27):
a theater. In theater, you can create a few interesting effects.
Generally your options are limited to things like lighting tricks,
maybe some creative sets or costumes, maybe an even a
stage illusion or two, and perhaps some sound design. But
with film there were other possibilities, and one fellow who
recognized those possibilities was the French filmmaker and illusionist George Mellier.
(09:53):
He was born in Paris, You know Paris in eighteen
sixty one. Let that sink in for a moment. This
man was born while the Civil War was going on
in the United States. He became interested in stagecraft and magic,
and by the eighteen nineties he was a successful stage magician.
In eighteen ninety five, he saw an early film exhibition
(10:14):
made by the Lumier Brothers and he became entranced by
this new medium. His experience and illusions encouraged him to
find ways to experiment with film to achieve new effects,
stuff that wouldn't be possible to do in the real world.
He was a special effects and film pioneer. He established
methods to shoot slow motion, stop motion animation, to do dissolves,
(10:37):
and tricks like superimposition and double exposure. Around eighteen ninety eight,
Melier had a really cool idea. He wanted to create
a truly bizarre special effect in which an actor would
appear to remove his own head on screen. But how
would he accomplish this? While the secret was in shooting
multiple exposures of the same real film. Typically, after you
(11:01):
expose film to light, you want to avoid doing that
again because you will interfere with that chemical record. You know,
if you were to ever take photographs with a film
camera and then someone were to open up the back
of the camera and expose the film to regular light,
you could potentially ruin shots that were already made, plus
(11:21):
ruin the film for the next couple of shots. It's
not something that you typically want to do. More light
will cause further reactions, chemical reactions on the actual plastic film,
and your shot gets ruined. If you've ever used the
cameras that don't quite line up the film properly at
the very beginning or the very end, you might even
notice that a couple of photos on those sections of
(11:44):
the film role have two sets of images super imposed
on top of one another, and that's because that little
section of film was exposed more than once. Melia did
this on purpose. He would set up a shot and
he would use a lens that had some of the
lens blacked out so that light could not pass through
(12:06):
that part of the lens. And we refer to this
as a mat matte, and you can think of it
like a mask for the lens, and that would mean
a section of each frame corresponding to that part of
the mat would remain unexposed to light. He would shoot
the scene as rehearsed. Afterward, he would rewind the exposed
film in the camera, beat it right back in as
(12:27):
if he was going to shoot something all for the
first time, and he would then replace this mat with
a new one and the new mat would block out
everything except the section that previously was unexposed. So in
other words, the part that was black would now be clear,
and the rest of the lens that was previously unblacked
(12:50):
would be blacked. So you replace one mat with a
different one. So he would then be able to film
something totally new into this same role of film, and
this time the would pick up a new scene and
by changing things between one section and the other, he
could create weird effects like the head removal trick. It
would appear as though all of this was shot at
the same time on the same role of film, but
(13:13):
in fact, through careful control of where the light would go,
Melia would use the same film twice or more to
produce cool results. And if you want to see an
example of what I'm talking about, and I highly recommend
you check this out because it is amazing even today,
go to YouTube and do a search for the short
film four Heads Are Better than One. The creativity of
(13:37):
this film, which by the way, lasts less than a minute,
is still astonishing. To say his experimental work was influential
would be a gross understatement. Other filmmakers, inspired by the
work of Melia tried new techniques that built upon the
foundation he established. For example, filmmaker and documentarian Norman Dawn
(13:59):
wanted to show films at historic buildings around California, but
several of those buildings had been damaged or even partly destroyed.
Other historic buildings had modern stuff like light poles in
front of them. He didn't want that to be in
the shot, so he wanted to show the buildings as
they had appeared in their original form before the decay,
(14:21):
before modern technology had advanced into the area. So he
came up with a really clever idea. Dawn placed a
pane of glass between the camera and the scene he
wanted to shoot, and on that pane of glass he
had paintings to enhance the scene. If a building's roof
had caved in, he would frame up the shot and
(14:43):
then have an artist paint a roof on the glass
so that when viewed through the camera, the painting and
the building behind it would line up and the building
would appear to be whole again. Or he might want
to cover up stuff like those telephone poles. He would
have an artist paint trees on the so from the
camera's perspective the polls were hidden. His process also involved
(15:05):
double exposures. This was an example of a Matt painting,
and he would claim credit for inventing this, and he
even applied for a patent on it. But subsequent lawsuits
established that other filmmakers were using similar approaches, and the
patent office ultimately denied the claim, but Matt paintings would
become an important part of filmmaking from that point forward.
(15:26):
One disadvantage to these early film effects was they required
the camera to remain stationary through the whole process. You
couldn't move the camera at all, or else your shots
wouldn't line up, so you wanted the camera to remain
in one place through all of these different exposures. Another
problem was that no action could cross the Matt line
(15:47):
because it would get cut off as it moved beyond
that invisible at least from the audience's perspective line. Now,
let's move on up to nineteen eighteen, when a guy
named Frank Williams created the Williams process, which honestly seems
pretty convenient to me. The Williams process allowed for more
(16:07):
movement and involved shooting actors against a solid background such
as a black or blue curtain on very high contrast film.
The process sometimes required multiple transfers onto new film until
you arrived at a black silhouette against a pure white background,
the negative image of what you were shooting before, and
(16:28):
this was called a holdout matt. The way these transfers
typically would work is that you would put one strip
of shot developed film into a camera, so you've already
shot on it, but you're putting it through the camera again.
And you would put a second strip of film that
is unshot, it's unprocessed, no lights hit it, and put
(16:49):
it right up against the first developed piece of film.
You would shine light through the camera and you would
let it just run. And this way you would transfer
for the images from one strip to the other. And
this was called bypacking because you were putting two different
pieces of film through the camera to achieve this process.
(17:12):
And you could also do this not just with developed
film where you're making copies. You could do it with negatives.
You could do it in a way to increase contrast
from copy to copy until you were able to create
a holdout mat reverse printing. The holdout matt creates a
white silhouette on a black background or a cover mat.
(17:33):
So now you've got a holdout matt and a cover mat.
You would take the footage of a previously shot background.
Let's say it's a foreboding forest, so you've shot your
actors in a sound stage, but you want the background
to be this really scary looking forest, and you would
bypack a film camera with the background footage that you
had shot and the black silhouette holdout matt of the
(17:56):
actor's footage that you shot. Then you would transfer this
combination to a third piece of unexposed film by again
shining a light through those other two pieces. And because
the background on the holdout mat is white, the light
passes through it easily and it hits the previously shot
background image that comes through and gets copied onto the
(18:17):
blank film. The silhouette of your actors is black that
prevents light from passing through. So the previously blank third
piece of film now has a background image and this
dark silhouette of actors moving through the frame. Then you
would have to take that piece of film that has
this black silhouette and you have to bypack it with
(18:39):
the original footage of the actor, not the silhouette, but
the actual actor footage. And now the real actor is
on top of the silhouette and appears to actually be
in front of whatever the background image is, in our case,
the foreboding forest. Because this type of matt moves from
frame to frame, it's called a traveling mat. And if
you remember Fraggle Rock you might remember Traveling Matt is
(19:02):
the name of Gobo's uncle. Gobo, by the way, is
another stage and lighting term. It stands for a template
or stencil that controls the shape of a lamps emitted light.
So some of the Fraggles had fun industry names, Gobo
and traveling Matt. When we come back, we will continue
down the history of how chroma key came about. But
(19:26):
first let's take a quick break. Before the break, I
was talking about the Williams process, but C. Dodge Dunning
would improve upon the Williams process by using yellow light
to shoot the actor in front of a blue screen,
(19:48):
creating the Dunning process, and this was used extensively in
the classic nineteen thirty three film King Kong, and they
weren't great for black and white film. Remember this is
before anyone was shooting on color. So although I mean
there were ways of treating film to create color, but
this was standard black and white film, so you didn't
have to worry about the weird lighting. But if you
(20:10):
wanted to shoot in color, that was going to cause
or require other considerations. Around the same time, engineers were
developing the optical printer, which really simplified the process of
transferring images from one strip of film to another. Now
I talked about bypacking, but the optical process could be
(20:31):
an alternative to that. It didn't eliminate it, but it
was a different way to achieve the same thing. Essentially,
an optical printer has a projector on one side and
a camera on the other. The projector shoots out a
projected image that then gets copied onto a new, unexposed
role of film inside the camera. And it also allowed
filmmakers to create new effects by changing the focal point
(20:54):
of the camera or the distance between the projector and
the camera. And rather than bypacking camera, you just use
this process you could get better results. The first mass
produced optical printer hit the market in the mid nineteen forties.
It came from a company called Acme Donne. In addition,
filmmakers created rear projection backgrounds, so in these actors would
(21:15):
perform in front of a screen like a projection screen,
not a green screen or a blue screen, and behind
that screen would be a film projector and it would
provide a projected background image. You could do this in
place of the processes have already described, putting your actors
in front of a screen that shows whatever background you wanted.
(21:37):
The background could be fairly static, but didn't have to be.
You could include a background that was actually dynamic, showing movement.
It could be a film in of itself. This was
used a lot in shots where people were in vehicles
and talking with one another. So rather than setting up
a car on a trailer and shooting it in the
real world with the camera on the trailer, or worse yet,
(21:59):
trying to figure out how to fit a camera onto
a real moving car that's operated by an actor, you
would typically have performers sitting in a stationary vehicle and
the screen behind and sometimes to either side of them
would display previously shot footage of scenery going by from
the correct perspective, as if the car were driving down
(22:19):
the road. This wasn't necessarily convincing, mind you, but it
was an interesting technique. In nineteen thirty two, engineers created
a process to produce films in color called appropriately Technicolor. Interestingly,
in this process, images would be captured to three strips
of black and white film at this stage as the
(22:40):
tri strip approach. This was not the original version of Technicolor.
It was technically the fourth incarnation of the Technicolor technology,
but it's the important one for our discussion. So how
do you produce a color image if you're using black
and white film as your medium? Well, first you have
to shoot your footage. And inside an early Technicolor tri
(23:04):
strip camera behind the lens was an optical cube and
it acted as a prism. Prisms break up incoming light
into bands of frequencies, and you've likely had one, or
played with one, or at least seen one. That's the
kind of stuff, you know. A light goes through it
and then it makes rainbows. You see a little rainbow
pattern projected somewhere. This prism would break up the incoming
(23:28):
light into three general bands that corresponded with red, green,
and blue. Each of those bands of light would hit
one of three strips of black and white film inside
the camera, so one strip of film would be exposed
to all the red light coming from a scene, one
from all the green light coming from a scene and
one from the blue. The concentration of each color in
(23:49):
the scene would affect how much light was hitting each
strip of film, So you'd end up with three negatives
of your scene that were all perfectly synchronized, all of
them in black and white, but each with different levels
of brightness for different objects. It all depended on what
color the objects were in the scene. A red chair,
(24:11):
for example, would appear as a very prominent image on
the black and white film that was hit with the
red light, while it would be less noticeable in the
green and blue strips. Now you would develop the negatives,
and you would process the film, the three strips of film,
and you would print them just as you would a
regular black and white movie, and you would technically have
(24:32):
three identical black and white sequences that only well, not
identical because the brightness would be different between each, but
they would be of the exact same shot. You would
then process these film strips by dying each of them
in their respective color, so you would literally end up
with a red tinted strip of film, blue tinted strip
(24:55):
of film, and a green tinted strip of film. Then
you would take these three died strips of film, and
you would laminate them together and you would print that
to a new role of film and you would have
a color motion picture which was fairly accurate, although the
technical process would evolve over time to become even more so.
(25:16):
And the Technicolor process is really what set the stage
for the next part of our story. It's why I
felt the need to even explain how it worked. Now
we get to a guy named Lawrence Larry Butler. He
was born in nineteen oh eight and he was actually
a second generation optical effects professional. His father, William Butler,
had been a silent film actor who frequently appeared in d. W.
(25:39):
Griffith films. Larry worked on several motion pictures in the
nineteen thirties before creating a new compositing process in nineteen
forty for the film The Thief of Baghdad. In that film,
Butler introduced a new special effect approach and this would
be the birth of the blue screen. All right, So
let's break down this process, and it builds on Technicolor
(26:01):
as I mentioned. So with Technicolor, you get three prints
of your shot, right, one for red, one for green,
one for blue. If you created a solid backdrop in
one of those three colors and shot something in front
of that background. You could use that particular strip of
film to create a traveling mat. Remember, the color would
(26:22):
show up as very bright in your black and white
film print because a lot of light is reflecting off
of that particular color. Effectively, you could make a negative
image of whatever the foreground was. The stuff you're shooting
would be dark and the background would be bright. You
would have to make sure that nothing in the scene
(26:43):
had the same color, however, or else your traveling matt
would effectively have holes in it because the color of
the foreground would match the color of the background. You've
probably seen this if someone's ever worn a shirt that's
the same color as whatever screen they're supposed to be
standing in front of. The same thing would even happen
in film. It's just that it would happen well in
(27:05):
advance of anyone being able to see it happen, like
see the effect of it. Because you had to do
all this other processing. The other two strips of black
and white film would have pretty dark backgrounds because the
light projected onto them wouldn't match the color of the backdrop. Right,
And you could take the film of a background shot.
This is called the background plate. So this is previously
(27:26):
shot film of whatever it is, whatever setting you're planning
on putting this stuff, and then you use the traveling
mat against it in an optical printer, and that would
produce a silhouette of the foreground action. And it's that
black hole that's the shape of whatever it was you
were shooting. And you would take this new print in
which you've got the silhouette of your action, it's the
(27:46):
previously filmed backdrop, and combine that with the processed color
film to fill in that hole left by the traveling mat.
So you've got this possibility now of creating a traveling
mat by taking advantage of the technicolor process. But then
you have to make a decision which of the three
colors should be the focus. Whichever color you choose is
(28:06):
going to determine what you can shoot, because you can't
have any objects or people in the scene that have
that color on them, or the traveling matt won't work properly.
This is what I mean when I say, if you've
ever seen someone on screen who's had a background effect
bleed onto them because the color of clothing they're wearing,
what was letting it happen. You've seen that issue. So
(28:30):
Butler decided to go with blue as the backdrop color,
largely because he determined it was a color far removed
from skin tones, and he wanted to make sure that
actors wouldn't match the color of the background and mess
everything up. So as long as you weren't shooting anything
blue in the foreground, you could use this process to
make a composite image of the foreground action against a
(28:51):
different background. He also would combine the blue negative image
with the green positive or processed image to create a
better tracking matt, something a more solid silhouette. In other words,
Butler's contribution led to him winning an Academy Award for
this process. Still, this was an incredibly time consuming approach.
(29:12):
I'm sure you gathered that just from my explanation of it.
Because you had to shoot your sequence, you had to
create the traveling matte negative, you had to combine that
against the background footage, and you had to combine that
combination of the background image and the traveling matt with
the fully processed color image and then ultimately come up
with a composite piece of film. It gave filmmakers way
(29:37):
more options when making movies. It allowed them to shoot
stuff inside a sound stage rather than whatever location they
would have to go to, and it even opened up
locations that would otherwise be impossible. But it did require
a lot of post production time and work. It also
required a close attention to lighting, otherwise you would end
up with blue halos around people and that was pretty
(30:00):
aren't distracting. In fact, all of these different approaches required
really good lighting, sometimes really intense lighting, so it would
also create pretty uncomfortable shooting conditions. It would get really
hot in those sound stages. So while it was phenomenal technology,
it required a lot of finesse to use it properly,
and a human touch was absolutely necessary through every stage
(30:21):
of the process. Now, over the next several years, really decades,
movies benefited from this technology. The tech allowed filmmakers to
do all sorts of neat things. Not only could they
make it seem like actors were in places that would
be hard or difficult to shoot in or places that
maybe don't even exist, they also allowed for stuff like
(30:42):
the incorporation of animation and live action in a way
that wasn't really possible. Before I'll get back to that again,
in a second. But in the early nineteen fifties, Eastman
Kodak created the color motion picture film that simplified the
process of shooting on color significant So, rather than exposing
three strips of black and white film to different bands
(31:04):
of light and then processing them to create a composite
color image, this new film actually contained all the layers
that corresponded to blue, green, and red. They each had
essentially filters and dyes in them, and each layer effectively
had its own silver halide crystals and respective dyes, and
streamlining the process for shooting on and developing color film.
(31:26):
You just had to have one strip, not the tri
strip approach of Technicolor. It really changed things. Also, by
tweaking the blue screen process, some inventors were able to
get spectacular results. This gets us back to that live
action and animation discussion. That would be Petro Vlajos, who
was the engineer who worked on a little film called
Mary Poppins in the early nineteen sixties. Vlahos wanted to
(31:49):
improve upon the technology that Butler had created, and one
of the issues he sought to address was that the
color blue used for blue screens wasn't a specific wavelength
of light. You got to remember that the wavelength of light,
or if you prefer the frequency of light, the two
are related, determines the light's color, the color that we perceive,
(32:10):
and the wavelengths corresponding to The blue screens of the
day ranged from four hundred and thirty five nanometers to
five hundred nanometers, and that meant any color blue that
fell in or near that range was off limits for
use in a scene. Vlajos figured there had to be
a better way, and he decided to use a different
backdrop color entirely yellow, but not just any yellow. He
(32:32):
wanted a precise yellow, the yellow that comes from sodium
gas discharge lamps. When you excite sodium gas, essentially when
you energize it with electricity, the gas gives off a
distinct yellow light with a wavelength of five hundred eighty
nine nanometers. As long as nothing in the camera frame
matches that precise shade of yellow, you could have all
(32:53):
sorts of colors in the shot, including different shades of yellow,
and not have to worry about skimping on things like
blue costume pieces. Paired with this was a customized camera
that contained a prism that could isolate the five hundred
and eighty nine wavelength of light. Vlahos was able to
produce an incredibly precise and accurate traveling matt this way,
(33:15):
which meant Disney could place actors on any separate background
without worrying about the effect showing at the seams. In fact,
in one sequence, Mary Poppins is wearing a hat that
has this veil like material on it, and you can
actually see the background, the anime background, through the veil,
and that's because of the precision of this approach. There
was one small hiccup, which was that Vlahos only had
(33:38):
one working prism that could isolate this specific band of light,
this five hundred and eighty nine nanometer band of light,
so they only had one sodium vapor camera as a result. Now,
when we come back, we're going to look at the
further evolution of this technology, including how it has changed
(33:58):
once the digital realm because came a reality. But first
let's take another quick break. I've stuck with the film
world for this podcast so far, but i also have
to talk about the use of chroma key technology in
(34:18):
the world of live television. See Mary Poppins came out
in nineteen sixty four, but the first use of chroma
key on live TV was in the late nineteen fifties.
This is the same technology that would become the basis
for TV weather reports, where the meteorologist stands in front
of a wall which seems to have a dynamic map
on it that can change from one image to the next.
(34:40):
But if the process I've described required so many steps,
if you had to do so much post production on
the film, how could you take that same basic idea
and make it work in the realm of television, in
real time live broadcast. Frank Gaskins and Mitt Altman led
this effort at NBC in the nineteen fifties. They created
(35:00):
a television camera approach to chroma key and tested it
out in nineteen fifty seven with a live broadcast of
Matinee Theater. The specific story they chose to serve as
the first experiment here was an adaptation of The Invisible Man,
and that was fitting because the nineteen thirty three film
adaptation of The Invisible Man had relied heavily on the
(35:22):
old Williams process. The live television version initially relied on
two cameras. One camera would capture a background image, the
other camera would be the four ground camera that would
be for all the action in the sequence, and behind
all this action would be a blue backdrop. Combining these
two sets of images simultaneously in a device called a
(35:45):
chroma key amplifier would create a live composite video. Feed.
Engineers at RCA created the actual technology, and I think
it's best if I just quote directly from the nineteen
fifty eight edition of the journal Electronic Ada that describes
this process. So here's a quote. A switching signal or
a color key used in association with the special effects amplifier,
(36:09):
controls the signals sent out over the air. The switching
signal is in turn created by the camera photographing the
live action in front of the blue screen. While the
camera is scanning the blue screen, the switching device automatically
activates the second camera, which projects the background. When the
scanning signal reaches an area covered by the live actors,
(36:31):
the switching device turns off the camera projecting the background
material and transmits the action. Now that's the end of
that quote. You could also feed images directly to the
chroma key amplifier. It didn't have to be a live
video from a second camera, so you could provide an
image like a map, allowing a meteorologist to stand in
front of it otherwise blank blue or green screen and
(36:53):
gesture at various regions. The audience at home would see
the meteorologist appearing to stand in front of the map,
or may be a summary of the forecasted whether for
the week, and not just a blue screen or a
green screen. Around the nineteen seventies, that's when we started
to see a gradual shift, particularly in television, from blue
screens to green ones. Part of that was because of
(37:16):
a very slow transition into digital technology. It would become
more important as digital cameras became a thing. Digital cameras
were better attuned to doing this with greens rather than
with blues, although you can do either. But another big
reason was just that people don't tend to wear a
lot of green, whereas blue was a pretty and still
(37:37):
is a pretty popular color. And once in a while
someone on camera would forget that they're wearing blue, and
then they'd step in front of a blue screen and
suddenly their jacket or their shirt or their tie or
whatever would become part of the background image. Back to
film for a moment, we're gonna leave TV for a second.
In nineteen eighty a guy named Richard Edlund, who worked
(37:59):
on a little film called The Umpire Strikes Back, made
another big contribution to the chroma key process Edluin developed
a quad optical printer which both sped up the process
for producing composite film shots and also brought the price
down as well. I mean, if you think about it,
saving time means saving money. He also developed a computer
(38:22):
controlled system of cameras which allowed for very precise camera movements,
and that meant you could create choreographed shots of foreground
and background and composite them together and have them match
up perfectly. It was also really effective for processing images
that were shot with miniatures, which was done a lot
in the original Star Wars series. So it was still
(38:43):
a painstaking process, but now a lot more could be
done on one piece of equipment per pass, as opposed
to having to do a process on a piece of equipment,
then do it again and then again and again until
you finally got whatever result you were after. Gradually, software
would creep into the realm of film and video effects,
(39:03):
and this leads us to a version of chroma key
that I think is actually the easiest to understand. It's
technically advanced, but the principle is simple. So let's say
that you want to do a Twitch stream and you're
playing a video game live, and you want your viewers
to see you sitting in front of the video game footage.
(39:24):
So once to make a dynamic background, a video gameplay
behind you. So you go out and you buy a
green screen and you set it up behind your gaming chair.
You throw up some lights more on that in the second,
and you launch a program that will insert your video
game capture as a custom digital background. Your viewers will
(39:45):
see you sitting in front of a screen otherwise filled
with I don't know, Skyrim or Minecraft or the untitled
Goose game or whatever it is you're playing. What's going
on on a technical level, Well, the digital world is
different from the analog world in lots of ways, but
importantly for our discussion, it comes down to how in
(40:05):
the digital world everything ultimately boils down to numeric values.
You or I could have a debate about whether a
particular color is aquamarine versus arrow blue, versus blue green
versus dark cyan, or whatever it may be. But in
the digital world, every color ultimately has a numeric value.
(40:29):
Assuming whatever we're looking at is a solid color, you
could designate that solid color with a specific numeric value
in computer software and then replicate it or immediately identify
it within any scene you might see where I'm going here.
With video software, you can designate a specific color from
one video source. This specific color is the chroma, as
(40:54):
it were, and this is the color you want to
replace or key Outdo software analyzes information that's coming from
say a digital camera feed into your computer, and it
looks for any signals that map to the value or
values of the color or colors you've picked. Most software
lets you fine tune this, so you can adjust the
(41:16):
settings to hone in on the specific shade of green
or blue or whatever it is that you plan to
key out. Anything that matches that value or range of
values then gets turned into a transparent video layer. The
secondary image in our case, the video game footage that
we're creating as we're playing this game shows through this
(41:40):
transparent layer, and you can actually think of the foreground
video as an overlay on top of the digital background
layer the video game footage. Anything transparent in that overlay
will show the background through the solid stuff presumably you,
the Twitch player will block the background image so viewers
(42:03):
will be able to see their favorite Twitch streamer sitting
in front of a video game. The software does all
the work for you, creating the composite video feed that
the viewer sees. That software, by the way, isn't Twitch itself.
Twitch is a video streaming platform, but to actually do
these sort of effects, you'd need to use some other
piece of software, such as some version of open broadcaster
(42:25):
software or OBS. And there are a lot of different
versions of video broadcasting software available for folks to play with,
from free stuff to professional grade stuff. This type of
versatility is the kind of stuff that previously you would
have had to have worked in like a TV studio
to have access to, but now anyone with a sufficiently
beefy computer can run this kind of operation. For this
(42:47):
to work well, you'd want to have really good lighting,
both for the foreground and for the background drop. You
want the lighting on the green screen you're using to
be nice and even, and you want to eliminate any
chef because if you're casting a shadow on the green screen,
the camera will pick up that part of the green
screen as being a darker color and it might even
(43:10):
be dark enough that the video software doesn't identify it
as the color that you want to key out, So
in those cases you would get these weird video artifacts
on screen. As a result, it'd be really distracting. So
ideally you want lights that illuminate the green screen evenly
and are dedicated just for that purpose. If you're lighting
yourself directly from the front, you're not using a ring
(43:32):
light or anything like that, then you're going to be
casting a shadow behind you, unless your Peter Pan, in
which case I guess you just think happy thoughts. Now,
this flies for stuff like Zoom meetings and Twitch streams,
but when it comes to professional grade film, it's not
really up to snuff. Software can do a bulk of
(43:52):
the work, but good old human effects artists are still
needed to make sure everything is coming out well. They
can step in and do some quality control, can tweak
things that can fix any issues that pop up, and
that pays off. You've probably seen a movie that had
phenomenal attention to this process and the effects are top notch,
and you've probably seen other movies where, due to whatever reason,
(44:14):
maybe it was budget, maybe it was just the talent
of the people working on it, you could tell that
such care wasn't given to the process, and it shows
in the final product. I still think films like Jurassic
Park I'm talking about the original Jurassic Park hold up
pretty darn well. And part of that is that the
movie depended on a mixture of different effects. Some of
(44:35):
them were computer generated and keyed in, some were robotic effects.
But a lot of this has to do with the
fact that the effects team as a whole took tremendous
care to produce results that were really convincing to the eye.
And that's the story behind chroma key and green or
blue screen technology. It's a super interesting approach to creating
(44:56):
a composite moving image, and frankly, there's going to be
a lot of other topics are around this that I
can go into. I could probably talk even more about
optical printers, for example, and the various approaches to film processing.
And you can see that while the actual chroma key
process is very different between film and digital video, the
(45:17):
basic idea of replacing one color or one element in
a shot with something from a totally different source remains
the same. It's the same underlying principle. No matter what
the actual process is. Yeah, yeah, this this screen bean
cast role is tight, y'all. Oh my god, mashed potatoes?
(45:40):
Who invented mashed potatoes? That give that person all the
Nobel prizes? Okay, that's it for the classic episode tech
Stuff in front of the grade screen. I hope you're
having as filling a Thanksgiving as I am. It's great,
very thankful for you, every one of you. I'm gonna
(46:02):
go take a nap, and next week we'll be back
with all new episodes. That should be very well rested
because I planned to sleep for about eighteen hours. Take care,
and I'll talk to you again really soon. Tech Stuff
(46:23):
is an iHeartRadio production. For more podcasts from iHeartRadio, visit
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your favorite shows.
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Hosts And Creators
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Karah Preiss
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