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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def render_to_image_file( self, image_out_path, width_pixels=None, height_pixels=None, dpi=90 ):
 """Render the SubjectInfo to an image file. Args: image_out_path : str Path to where image image will be written. Valid extensions are ``.svg,`` ``.pdf``, and ``.png``. width_pixels : int Width of image to write. height_pixels : int Height of image to write, in pixels. dpi: Dots Per Inch to declare in image file. This does not change the resolution of the image but may change the size of the image when rendered. Returns: None """

        self._render_type = "file"
        self._tree.render(
            file_name=image_out_path,
            w=width_pixels,
            h=height_pixels,
            dpi=dpi,
            units="px",
            tree_style=self._get_tree_style(),
        )