'Max number of proposals (to pad to) for each image in the input batch.
At training time, this is set to be the `second_stage_batch_size` if hard
example miner is not configured, else it is set to
`first_stage_max_proposals`. At inference time, this is always set to
`first_stage_max_proposals`.
Returns:
A positive integer.'

@property
def max_num_proposals(self):

    if (self._is_training and (not self._hard_example_miner)):
        return self._second_stage_batch_size
    return self._first_stage_max_proposals
