4-Image

# 4-Image - Feature Based Image Metamorphosis Beier and Neely...

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Image Compositing and Morphing Jason Lawrence CS 4810: Graphics Feature Based Image Metamorphosis , Beier and Neely 1992 Acknowledgement: slides by Misha Kazhdan, Allison Klein, Tom Funkhouser, Adam Finkelstein and David Dobkin

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Outline • Image Compositing o Blue-screen mattes o Alpha channel o Porter-Duff compositing algebra • Image Morphing
Image Compositing Separate an image into “elements” o Render independently o Composite together Applications o Cel animation o Chroma-keying o Blue-screen matting Bill makes ends meet by going into flm

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Blue-Screen Matting Composite foreground and background images o Create background image o Create foreground image with blue background o Insert non-blue foreground pixels into background
Blue-Screen Matting Composite foreground and background images o Create background image o Create foreground image with blue background o Insert non-blue foreground pixels into background Problem: lack of partial coverage results in a haloing effect along the boundary!

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Encodes pixel coverage information o α = 0: no coverage (or transparent) o α = 1: full coverage (or opaque) o 0 < α < 1: partial coverage (or semi-transparent) Single Pixel Example: α = 0.3 Alpha Channel Partial Coverage Semi- Transparent or
Compositing with Alpha Controls the linear interpolation of foreground and background pixels when elements are composited. α = 1 0 < α < 1 α = 0 0 < α < 1

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Pixels with Alpha • Alpha channel convention: o (r, g, b, α ) represents a pixel that is α covered by the color C = (r* α , g* α , b* α ) »Color components are pre-multiplied by α »Can display (r,g,b) values directly • What is the meaning of the following? o (0, 1, 0, 1) = ? o (0, 1/2, 0, 1) = ? o (0, 1/2, 0, 1/2) = ? o (0, 1/2, 0, 0) = ?
Pixels with Alpha • Alpha channel convention: o (r, g, b, α ) represents a pixel that is α covered by the color C = (r* α , g* α , b* α ) »Color components are pre-multiplied by α »Can display (r,g,b) values directly • What is the meaning of the following? o (0, 1, 0, 1) = Full green, full coverage o (0, 1/2, 0, 1) = ?

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4-Image - Feature Based Image Metamorphosis Beier and Neely...

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