def _image_id_to_filename(image_id:int) -> str:
    """
    convert image_id to the corresponding filename of the image in COCO2017

    Parameters
    ----------
    image_id: int,
        the `image_id` of the image, read from the annotation file
    
    Returns
    -------
    fn: str,
        the filename of the corresponding image
    """
    fn = f"{image_id:012d}.jpg"
    return fn