    //! Fill pixel values along the Z-axis at a specified pixel position \overloading.
    CImg<T>& fillZ(const unsigned int x, const unsigned int y, const unsigned int c, const double a0, ...) {
      const ulongT wh = (ulongT)_width*_height;
      if (x<_width && y<_height && c<_spectrum) _cimg_fill1(x,y,0,c,wh,_depth,double);
      return *this;
     
    CImg<T>& fillZ(const unsigned int x, const unsigned int y, const unsigned int c, const double a0, ...) {
      const ulongT wh = (ulongT)_width*_height;
      if (x<_width && y<_height && c<_spectrum) _cimg_fill1(x,y,0,c,wh,_depth,double);
      return *this;