Return `Image` object created from image in file `fn`.

def open_image(fn:PathOrStr, div:bool=True, convert_mode:str='RGB', cls:type=Image,
        after_open:Callable=None)->Image:
    "Return `Image` object created from image in file `fn`."
    with warnings.catch_warnings():
        warnings.simplefilter("ignore", UserWarning) # EXIF warning from TiffPlugin
        x = PIL.Image.open(fn).convert(convert_mode)
    if after_open: x = after_open(x)
    x = pil2tensor(x,np.float32)
    if div: x.div_(255)
    return cls(x)