1. Copyright  Pat Hanrahan Composing Two Elements Background ForegroundTraveling Matte Holdout Matte * *+ += =

2. Copyright  Pat Hanrahan Optical Printing From: “Special Optical Effects,” Zoran Perisic From: “Industrial Light and Magic,” Thomas Smith (p. 181)

3. Copyright  Pat Hanrahan “Pulling a Matte” - Matte Creation From digitized images o Blue-screen matting (Petro Vlahos) Separate blue background from foreground image o Video or chroma-keying Range of chromaticities marked transparent o Image processing Set of colors marked transparent, region growing... From computer generated images o Coverage o Transparency

4. Copyright  Pat Hanrahan Blue Screen

5. Copyright  Pat Hanrahan Blue-Screen Matte Extraction Given: C - Observed color at each pixel C B - Backing color (perhaps at each pixel) Compute: C’ F = (  F R F,  F G F,  F B F,  F ) Matte Equation C = C F + (1-  F ) C B (3 equations in 4 unkowns) B G K B=aG Vlahos Assumption CBCB C CFCF

6. Copyright  Pat Hanrahan Porter-Duff Compositing Algebra C’ = F A C’ A +F B C’ B OpenGL blendfunction Specify src and dst F’s 0, 1, As, Ad, 1-As, 1-Ad, min(As,1-Ad), Cs, Cd, 1-Cs, 1-Cd,

7. Copyright  Pat Hanrahan Painting – how are each of these strokes done?