_mid_point        618 Magick++/lib/Magick++/STL.h     double _mid_point;
_mid_point        636 Magick++/lib/Magick++/STL.h     double _mid_point;
_mid_point        590 Magick++/lib/STL.cpp   image_.level( _black_point, _white_point, _mid_point );
_mid_point        606 Magick++/lib/STL.cpp   image_.levelChannel( _channel, _black_point, _white_point, _mid_point );