1. Lynwood Dunn (1904-1998) Visual effects pioneer Acme-Dunn optical printer

2. The Over Operator How to indicate which parts of front picture are clear and which are opaque Use alpha channel to indicate opacity [Smith] Over operator [Porter & Duff S’84] A over B: C A over B =  A C A + (1 –  A )  B C B  A over B =  A + (1 –  A )  B Note that  A C A used in color eqs, so store  A C A instead of C A A over B w/premultiplied alpha C A over B = C A + (1 –  A ) C B  A over B =  A + (1 –  A )  B B A C = (  R  G  B  ) 25% transparent yellow 75% transparent blue ? C A over B =.75(1,1,0) +.25(.25)(0,0,1) = (.75,.75,0) + (0,0,.125) = (.75,.75,.125)  A over B =.75 +.25(.25) =.875 C ABW =.875(.75,.75,.125) +.125(1)(1,1,1) = (.66,.66,.11)+(.125,…) =(.78,.78,.24)

3. Academy of Motion Picture Arts & Sciences Scientific and Engineering Award To Alvy Ray Smith, Tom Duff, Ed Catmull and Thomas Porter for their Pioneering Inventions in Digital Image COMPOSITING. PRESENTED MARCH 2, 1996

5. Accumulating Opacity Depends on order of accumulation Back to front –Over operator C out =  C + (1 –  ) C in  out =  + (1 –  )  in –No need to maintain  Front to back –Under operator C out =  in C in + (1 –  in ) C  out =  in + (1 –  in )  –Need to maintain  C in,  in C out,  out C,  C out,  out C in,  in C,  view

6. Volume Rendering Methods Data stored as 3-D array of samples C – color  – opacity N – normal, etc. Splatting –“Forward:” voxels to pixels –Overlay planes from volume Ray casting –“Backward:” pixels to voxels –Ray marches from voxel to voxel from SGI’s Volumizer, 1999