def normalize_numpy(img_256_arr):
    """
    Normalizes an image NumPy array so its values lie in the range [0, 1]

    Args:
        img_256_arr: a NumPy array (intended to be 2D or 3D) whose values lie 
        in the range [0, 255], representing an image

    Returns:
        A NumPy array, with the same dimensions as the input, whose values lie 
        in [0, 1]

    """
    return img_256_arr / 255.0