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Digital Compositing

CS5245 Vision and Graphics for Special Effects

Leow Wee Kheng

Department of Computer Science

School of Computing

National University of Singapore

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Introduction

Introduction

Digital compositing means

digitally manipulated integration of at least two images to

produce a new image.

The new image must appear realistic.

It must be completely and seamlessly integrated,as if it were actually photographed by a single camera.

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Introduction

Example: A scene in Saint (1997) shot in front from blue screen.

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Introduction

Main Topics

Keying

Separate foreground elements from background elements.

Rig RemovalRemove unwanted elements in footage.

Alpha Blending

Blend foreground elements with new background footage.

Other topics: Refer to [Kel00].

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Alpha Blending

Alpha Blending

Basic equation

C = F + (1 )B (1)

F: foreground image

B: background image

C: composite: opacity or transparency

matte: an image of values

The above operation is performed on each corresponding pixel.

If = 1, then C = F,foreground is shown, i.e., foreground is opaque.

If = 0, then C = B,background is shown, i.e., foreground is transparent.

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