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Prepared by: AQ First Prepared on:1st September 2007 Last Modified on: -n-
Quality checked by: -n-
Copyright 2007 Asia Pacific University College of Technology and Innovation
Chapter 5:
Green Screen Technology
Digital Audio and Video(CT018-3-2)
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Learning Outcomes
At the end of this lecture YOU will be able to:
Demonstrate an awareness of green screen
technologies.
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The Green Screen
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The Green Screen
Chroma key compositing (orchromakeying) is a technique for compositing twoimages or frames together in which a color
(or a small color range) from one image isremoved (made transparent), revealinganother image behind it commonly used invideo production and post-production.
This technique is also referred to as colorkeying, color-separation overlay (CSO),greenscreen, and bluescreen.
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The Green Screen
Green screen technology is the basis of
the effects seen in everything from the
latest Hollywood blockbusters to the
weather forecast.
Make sure that you have a goodbackground, contrasting colours for
clothing & props and good lighting.
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The Green Screen
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History
For filmmaking, a complex and timeconsuming process once known as"travelling matte" was used prior to the
introduction of digital compositing. One drawback to the traditional traveling
matte is that the cameras shooting theimages to be composited can't be easily
synchronized
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History
Some films make heavy use of chromakey to add backgrounds that areconstructed entirely using computer-
generated imagery (CGI). Performancesfrom different takes can even becomposited together, which allows actorsto be filmed separately and then placed
together in the same scene. Chroma key allows performers to appear
to be in any location without even leavingthe studio.
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The principal subject is filmed or photographed
against a background consisting of a single color
or a relatively narrow range of colors, usually
blue or green because these colors areconsidered to be the furthest away from skin
tone.
The Process
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The Process
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The Process
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Blue vs Green
Green ScreenOn film, the green
layer has the finest
grain structure.
Image sensors indigital video
cameras are most
sensitive to green.
COMPARISON
Blue ScreenIs least
prominent in
skin tone.
The blue layerof film is
sharpest but is
also the
grainiest layer.
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The key to lighting a green screen is consistency. The
whole point is to create a single, consistent shade of
colour across the entire screen.
Diffusion filters are very handy when lighting green
screens. Diffusion helps create more even lighting and
reduce the impact of shadows.
Lighting Techniques
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Question and Answer Session
Q & A