y_truth = [batch, H, W, 2] (one-hot encoded)
logits = [batch, H, W, 2]
IOU, up_op = tf.metrics.mean_iou(
                 labels = argmax(y_truth, axis=3),
                 predictions = argmax(logits, axis=3),
                 num_classes = 2)

with tf.control_dependencies([up_op]):
    if create_scalar_summaries:
        tf.summary.scalar('IOU', IOU)