sub minmax { ( min(@_), max(@_) ) }  # helper function

for (@list_of_Num_Extraction) {
    if (/^(\d+),(\d+):(\d+),(\d+)$/) {
        my ($l,$r, $t,$b) = (minmax($1,$3), minmax($2,$4));
        for my $x ($l .. $r) {      # left to right
            for my $y ($t .. $b) {  # top to bottom
              $Unique_Num_List{($x-1)*$num_columns + $y} = "($x,$y)";
            }
        }
    }
    # and so on ...
}