MattingTodayHow does Superman fly?“Pulling a Matte”Blue ScreenBlue Screen mattingThe UltimatteBlue screen for superman?Semi-transparent mattesMatting Problem: Mathematical DefinitionWhy is general matting hard?Solution #1: No Blue!Solution #2: Gray or FleshTriangulation Matting (Smith & Blinn)The AlgorithmTriangulation Matting ExamplesMore ExamplesMore examplesProblems with MattingSlide 20Environment Matting EquationExplanation of FEnvironment MattesPerformanceHow much better is Environment Matting?Slide 26Movies!Matting15-463: Rendering and Image ProcessingAlexei Efros…with many slides from Kyros KutulakosTodayCatch up from last time•Video Textures for human actors (“Do as I do”)Blue Screen MattingEnvironment MattingHow does Superman fly?Super-human powers?ORImage Matting and Compositing?“Pulling a Matte”Problem Definition:•The separation of an image C into–A foreground object image Co, –a background image Cb, –and an alpha matte •Co and can then be used to composite the foreground object into a different imageHard problem•Even if alpha is binary, this is hard to do automatically (image segmentation problem)•For movies/TV, manual segmentation of each frame is infeasible •Need to make a simplifying assumption…Blue ScreenBlue Screen mattingMost common form of matting in TV studios & moviesPetros Vlahos invented blue screen matting in the 50s. His Ultimatte® is still the most popular equipment. He won an Oscar for lifetime achievement.A form of background subtraction:•Need a known background•Compute alpha as SSD(C,Cb) > threshold–Or use Vlahos’ formula: = 1-p1(B-p2G)•Hope that foreground object doesn’t look like background –no blue ties!•Why blue?•Why uniform?The Ultimattep1 and p2Blue screen for superman?Semi-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)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- )B + C ~ Color F ~ Foreground color B ~ Background color ~ Amount of light that passes through the foreground ~ Contribution of light from Environment that travels through the objectExplanation of R – 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
View Full Document
Unlocking...