From: thebretcahill@gmail.com   
      
   The derivative of any still shot would be blank.   
      
   The derivative of a mono chromatic background getting uniformly darker at a   
   const. rate would be a constant uniform background still shot.   
      
   What about the derivative of a point moving horizontally across the middle of   
   the screen at const. velocity?   
      
   That would be a still shot but of what?  A line or a point?  And where?   
      
   The math is similar to optical flow.   
      
   This would be a popular app.  After taking the derivative of a video of, say,   
   a dance floor you then integrate to recover the original moving objects.  Find   
   out who has the best moves . . .   
      
      
   Bret Cahill   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)