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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