I'm trying to form a gray-scale image of a scene by scanning it with a laser   
   in daylight.    
      
   The setup is, I stare at the entire scene with a stationary lens and a single   
   photodetector (and this does not scan, but takes in the entire scene), and   
   then I scan a laser spot across the scene to build up a rastered image.   
   The light contribution from the entire background is 8000X brighter than the   
   light from the laser spot.   
   I have heard that it is possible to extract faint signals from a noisy   
   background by modulating the signal (the laser spot) and extracting the   
   matching frequency components from the noise, which sounds crazy to me   
   because, well, the noise is 8000X    
   greater than the signal, and any detector is going to have a hard time seeing,   
   say, 1000 photons on top of 8,000,000.   
      
   What am I missing?  I'm not a signal-processing guy, if that wasn't obvious   
   already.   
      
   Can modulating the laser spot enable me to build up a grayscale image of the   
   scene, and if so, how, or should I take a different approach?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)