def _check_range(val_range, min_val=None, max_val=None):
    """ Check whether the range is a valid range.

    Args
        val_range: A pair of lower and upper bound.
        min_val: Minimal value for the lower bound.
        max_val: Maximal value for the upper bound.
    """
    if val_range[0] > val_range[1]:
        raise ValueError('interval lower bound > upper bound')
    if min_val is not None and val_range[0] < min_val:
        raise ValueError('invalid interval lower bound')
    if max_val is not None and val_range[1] > max_val:
        raise ValueError('invalid interval upper bound')
 Check whether the range is a valid range.

    Args
        val_range: A pair of lower and upper bound.
        min_val: Minimal value for the lower bound.
        max_val: Maximal value for the upper bound.
    
keras_retinanet/utils/image.py