def render_pdf_file_to_image_files_pdftoppm_pgm(pdf_file_name, root_output_file_path,
                                           res_x=150, res_y=150):
    """Same as renderPdfFileToImageFile_pdftoppm_ppm but with -gray option for pgm."""

    comm_output = render_pdf_file_to_image_files_pdftoppm_ppm(pdf_file_name,
                                        root_output_file_path, res_x, res_y, ["-gray"])
    return comm_output