    static CImg<T> get_load_pdf_external(const char *const filename, const unsigned int resolution=400) {
      return CImg<T>().load_pdf_external(filename,resolution);
    }
    static CImg<T> get_load_pdf_external(const char *const filename, const unsigned int resolution=400) {
      return CImg<T>().load_pdf_external(filename,resolution);
    }