### `tf.contrib.metrics.streaming_mean_iou(predictions, labels, num_classes, weights=None, metrics_collections=None, updates_collections=None, name=None)` {#streaming_mean_iou}
Calculate per-step mean Intersection-Over-Union (mIOU).
Mean Intersection-Over-Union is a common evaluation metric for
semantic image segmentation, which first computes the IOU for each
semantic class and then computes the average over classes.
##### IOU is defined as follows:
IOU = true_positive / (true_positive + false_positive + false_negative).
The predictions are accumulated in a confusion matrix, weighted by `weights`,
and mIOU is then calculated from it.
For estimation of the metric over a stream of data, the function creates an
`update_op` operation that updates these variables and returns the `mean_iou`.
If `weights` is `None`, weights default to 1. Use weights of 0 to mask values.
##### Args:
* `predictions`: A `Tensor` of prediction results for semantic labels, whose
shape is [batch size] and type `int32` or `int64`. The tensor will be
flattened, if its rank > 1.
* `labels`: A `Tensor` of ground truth labels with shape [batch size] and of
type `int32` or `int64`. The tensor will be flattened, if its rank > 1.
* `num_classes`: The possible number of labels the prediction task can
have. This value must be provided, since a confusion matrix of
dimension = [num_classes, num_classes] will be allocated.
* `weights`: An optional `Tensor` whose shape is broadcastable to `predictions`.
* `metrics_collections`: An optional list of collections that `mean_iou`
should be added to.
* `updates_collections`: An optional list of collections `update_op` should be
added to.
* `name`: An optional variable_scope name.
##### Returns:
* `mean_iou`: A `Tensor` representing the mean intersection-over-union.
* `update_op`: An operation that increments the confusion matrix.
##### Raises:
* `ValueError`: If `predictions` and `labels` have mismatched shapes, or if
`weights` is not `None` and its shape doesn't match `predictions`, or if
either `metrics_collections` or `updates_collections` are not a list or
tuple.