Algorithm

 Begin subroutine emask

   Determine maximum of exposure
   Multiply threshold parameters with exposure maximum

   Loop over image pixels 
     Set pixels of detection mask to 1 if exposure is above cutoff 
       and 0 otherwise.
   END Loop

   Loop over image pixels
     Set pixels of detection mask to 0 if gradient of exposure 
       is above threshold 
   END Loop

 End subroutine  emask