def gen_tf_bounding_boxes(boxes):
    """
        change (left, upper, right, lower) -> (offset_height, offset_width, target_height, target_width)
        Note: upper < lower, left < right
    """
    left, upper, right, lower = boxes
    offset_height = upper
    offset_width = left
    target_height = lower - upper
    target_width = right - left
    return offset_height, offset_width, target_height, target_width