Nov 06 2012

Green screen technology

I still have no landline after Hurricane Sandy brought down the tree and with it the phone line. So that means I will not have DSL and will have to follow the election results the old-fashioned way, on TV. I suspect that they will use a lot of gee-whiz technology.

I am fascinated in particular by ‘green screen’ technology, where people stand in front of a blank green screen and images are superimposed on them to create an illusion of one unified scene in which the person seems to be actually there in the projected surroundings. I have long meant to look into the physics of it more closely but never got around to it.

Nowadays TV news programs, especially on election night, tend to heavily utilize these effects and this short video from the BBC shows how it is done and the pitfalls for the presenter because of all the people involved, he is the one person who does not see what the rest of us see, though presumably there is a TV monitor off-screen to give him some idea of what is going on.


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  1. 1
    Argle Bargle

    Watch just about any TV meteorologist. They use green screen a lot and when they’re pointing to where the edge of the blizzard is, they always glance away from the camera to look at the monitor to make sure they’re gesturing at the right place.

  2. 2
    A. Noyd

    Then there are incidents like meteorologists who wear green ties.

  3. 3

    Remember tobacco-company-shill Cokie Roberts? Back in 1994, she and ABC got caught pretending she was outside the capitol in Washington when she was actually in a studio.


    Faking in a movie is one thing, but faking the “news” is…well, it’s standard procedure these days.

  4. 4
    F [i'm not here, i'm gone]

    I always enjoy seeing a presenter who has worn something of a shade of blue or green close enough to the color of the blue/green screen.

  5. 5
    F [i'm not here, i'm gone]

    Oh, and if you want to look into this a bit:

  6. 6
    Cathy W

    At our local children’s museum, they have a chromakey machine for the kids to play with, including T-shirts and big pieces of cloth dyed the proper shade of green to get replaced with the image. It’s one of the more popular exhibits.

  7. 7

    In the pre-electronic days, before video chromakey/bluescreen/greenscreen/CSO, it used to be done in film quite ingeniously. There were 3 colour layers on movie film: red, blue, and green. So they would just develop/print the red and green, leaving the blue transparent, so you could put any other film or stills you like behind it.

  8. 8

    Or one wearing something reflective so that the glancing angles reflect the green/blue screen.

    There’s a local weather presenter here who has a habit of wearing a thick, shiny black PVC belt so it ends up looking like she has an implausibly thin waist.

  9. 9
    Andrew James

    Green screen technology has been around for a number of decades already. We usually see this on weathermen with their projected background. But nowadays, it is becoming the basis of the effects seen on a number of Hollywood blockbusters. The idea here is simple. You shoot a video with a single colored backdrop (that is, green and sometimes blue). It allows you to make that color transparent and then, you can replace later on with any other video clip, graphic or still image.

  10. 10
    Andrew James

    Nowadays, Computer Generated Imagery has been widely used in performing the same technique that has been discovered years ago. With the incorporation of the newest technology, the chroma-keying are more convenient to utilize and presents a more flawless and realistic output on films. With most of sci-fi or fantasy films, green-screen or blue-screen technology is indeed a very helpful tool to make things amazing and out of the usual.

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