procedure blkzap( object, x1, y1, x2, y2 )

# procedure to mask out a rectangular region in images. Note that 
# this procedure runs on an object frame, but modifies the 
# BPM file named by the BPM header keyword! The user supplies
# two diagonal corners of the regions to be masked out. 
#
# Takes about 90 seconds / projected MOSAIC frame on Ultra-60
#
# Arjun Dey (from James Rhoads' satzap.cl)
# 08/04/99

string object  { prompt="Input image"}
real x1 { prompt="lower left corner: location 1 - X "}
real y1 { prompt="lower left corner: location 1 - Y "}
real x2 { prompt="upper right corner: location 2 - X "}
real y2 { prompt="upper right corner: location 2 - Y "}

begin
   string pdexp,x1s,y1s,x2s,y2s

   x1s=str(x1)
   y1s=str(y1)
   x2s=str(x2)
   y2s=str(y2)
   pdexp = "if ((x>="//x1s//")&&(x<="//x2s//")&&(y>="//y1s//")&&(y<="//y2s//")) then im1+1 else im1"

   print( pdexp )
   imgets( object, "BPM" )
   imcalc( imgets.value, imgets.value, pdexp, verbose+ )

end