img:=PPM.readPPMFile("lenaGrey.ppm"); // a grey scale image
median:=histogramMedian(histogram(img));
median.println();

bw:=PPM(img.w,img.h);
  // stream bytes from orginal, convert to black/white, write to new image
  // each pixel is 24 bit RGB
img.data.pump(bw.data.clear(),'wrap(c){ if(c>median) 0xff else 0  });

bw.write(File("foo.ppm","wb"));