fcn histogram(image){
   hist:=List.createLong(256,0);	// array[256] of zero
   image.data.howza(0).pump(Void,'wrap(c){ hist[c]+=1 });  // byte by byte loop
   hist;
}
fcn histogramMedian(hist){
   from,to:=0,(2).pow(8) - 1; // 16 bits of luminance
   left,right:=hist[from],hist[to];
   while(from!=to){
      if(left<right){ from+=1; left +=hist[from]; }
      else 	    { to  -=1; right+=hist[to];   }
   }
   from
}