def get_normalize(input_shape):
    """
    rescale keypoint distance normalize coefficient
    based on input shape, used for PCK evaluation

    NOTE: 6.4 is standard normalize coefficient under
          input shape (256,256)

    # Arguments
        input_shape: input image shape as (height, width)

    # Returns
        scale: normalize coefficient
    """
    #assert input_shape[0] == input_shape[1], 'only support square input shape.'

    # use averaged scale factor for non square input shape
    scale = float((input_shape[0] + input_shape[1]) / 2) / 256.0

    return 6.4*scale