    //! Crop image region \newinstance.
    CImg<T> get_crop(const int x0, const int y0,
                     const int x1, const int y1,
                     const unsigned int boundary_conditions=0) const {
      return get_crop(x0,y0,0,0,x1,y1,_depth - 1,_spectrum - 1,boundary_conditions);
     
    CImg<T> get_crop(const int x0, const int y0,
                     const int x1, const int y1,
                     const unsigned int boundary_conditions=0) const {
      return get_crop(x0,y0,0,0,x1,y1,_depth - 1,_spectrum - 1,boundary_conditions);