Matting and Transparency15-463: Computational PhotographyAlexei Efros, CMU, Fall 2006Midterm StatisticsSemi-transparent mattesWhat we really want is to obtain a true alpha matte, which involves semi-transparency• Alpha between 0 and 1Matting Problem: Mathematical DefinitionWhy is general matting hard?Solution #1: No Blue!Solution #2: Gray or FleshTriangulation Matting (Smith & Blinn)How many equations?How many unknowns?Does the background need to be constant color?The AlgorithmTriangulation Matting ExamplesMore ExamplesMore examplesProblems with MattingImages do not look realisticLack of Refracted LightLack of Reflected LightSolution:Modify the Matting EquationEnvironment Matting and Compositingslides by Jay HetlerDouglas E. Zongker ~ Dawn M. Werner ~ Brian Curless ~ David H. SalsinEnvironment Matting EquationC = F + (1- α)B + ΦC ~ ColorF ~ Foreground colorB ~ Background colorα ~ Amount of light that passes through the foregroundΦ~ Contribution of light from Environment that travels through the objectExplanation of ΦR – reflectance imageT – Texture imageEnvironment MattesPerformanceCalibrationMatting: 10-20 minutes extraction time for each texture map (Pentium II 400Mhz)Compositing: 4-40 frames per secondReal-Time?How much better is Environment Matting?Alpha Matte Environment Matte PhotographHow much better is Environment Matting?Alpha Matte Environment Matte
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