for my $i (0..$size-1){
      my $i_col = $i%0xFF;
      my $i_mod20_9 = $i%20>9;
      for my $j (0..$size-1){
         $USE[$i][$j] = $i_mod20_9^($j%20>9) ? $reds[$i_col] : $greens[$j%0xFF];
      }
   }