How to use the paperwork-backend.paperwork_backend.util.image2surface function in paperwork-backend

def __paint_img(self, pdf_surface, pdf_size, pdf_context, page,
                    preview=False):
        img = page.img
        if self.__process_func:
            img = self.__process_func(img)
        quality = float(self.__quality) / 100.0

        new_size = (int(quality * img.size[0]),
                    int(quality * img.size[1]))
        img = img.resize(new_size, PIL.Image.ANTIALIAS)

        scale_factor_x = pdf_size[0] / img.size[0]
        scale_factor_y = pdf_size[1] / img.size[1]
        scale_factor = min(scale_factor_x, scale_factor_y)

        img_surface = image2surface(img)

        pdf_context.save()
        try:
            pdf_context.identity_matrix()
            pdf_context.scale(scale_factor, scale_factor)
            pdf_context.set_source_surface(img_surface)
            pdf_context.paint()
        finally:
            pdf_context.restore()

logger.info("Rotating the page ...")
            img = img.rotate(90, expand=True)

        (width, height) = img.size

        # scale the image down
        # XXX(Jflesch): beware that we get floats for the page size ...
        scaling = min(
            print_context.get_width() / width,
            print_context.get_height() / height
        )

        logger.info("DPI: %fx%f" % (print_context.get_dpi_x(),
                                    print_context.get_dpi_y()))

        surface = image2surface(img)
        keep_refs['surface_cache_' + str(self.page_nb)] = surface

        # .. and print !
        cairo_context = print_context.get_cairo_context()
        cairo_context.scale(scaling, scaling)
        cairo_context.set_source_surface(surface, 0, 0)
        cairo_context.paint()