imaging - CS148: Introduction to Computer Graphics and...

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Page 1 CS148: Introduction to Computer Graphics and Imaging Image Compositing Colbert Challenge CS148 Lecture 14 Pat Hanrahan, Winter 2009 Key Concepts Optical compositing and mattes The alpha channel Compositing operators Premultipled alpha Matte extraction
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Page 2 Optical Compositing CS148 Lecture 14 Pat Hanrahan, Winter 2009 Image Composition Defn: Combine foreground element with background Examples: ± Graphics arts: masking tape, stencil, frisket ± Animation: cels, multiplane camera ± Film: optical printing, blue screen matting ± Video: chroma-keying ± Computer graphics: alpha channel
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Page 3 CS148 Lecture 14 Pat Hanrahan, Winter 2009 Multiplane Camera – Walt Disney http://disneyandmore.blogspot.com/2007/09/walt-disney-multiplane-camera-and.html CS148 Lecture 14 Pat Hanrahan, Winter 2009 Optical Printing From: “Special Optical Effects,” Zoran Perisic From: “Industrial Light and Magic,” Thomas Smith (p. 181)
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Page 4 CS148 Lecture 14 Pat Hanrahan, Winter 2009 Composing Two Elements Background Foreground Traveling Matte Holdout Matte * * + + = = The Alpha Channel
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Page 5 CS148 Lecture 14 Pat Hanrahan, Winter 2009 The Alpha Channel A alpha channel is an additional image that defines: ± The transparency or opacity of an image ± The presence or absence of imagery ± Geometric coverage: soft-edge
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imaging - CS148: Introduction to Computer Graphics and...

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