How to use Keras generator with tf.data API

Question

I am trying to use the generator found in Keras preprocessing library. I wanted to experiment with this since Keras provides great functions for image augmentation. However, I am not sure if this is actually possible.

Here is how I made a tf dataset from the Keras generator:

def make_generator():
    train_datagen = ImageDataGenerator(rescale=1. / 255)
    train_generator = 
    train_datagen.flow_from_directory(train_dataset_folder,target_size=(224, 224), class_mode='categorical', batch_size=32)
    return train_generator

train_dataset = tf.data.Dataset.from_generator(make_generator,(tf.float32, tf.float32)).shuffle(64).repeat().batch(32)

Note that if you try to directly give train_generator as the argument to tf.data.Dataset.from_generator there will be an error. However, the above method doesn't produce an error.

When I run it within a session to check the output from the dataset I get the following error.

iterator = train_dataset.make_one_shot_iterator()
next_element = iterator.get_next()
sess = tf.Session()
for i in range(100):
    sess.run(next_element)

Found 1000 images belonging to 2 classes. --------------------------------------------------------------------------- InvalidArgumentError Traceback (most recent call last) /usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py in _do_call(self, fn, *args) 1291 try: -> 1292 return fn(*args) 1293 except errors.OpError as e:

/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py in _run_fn(feed_dict, fetch_list, target_list, options, run_metadata) 1276 return self._call_tf_sessionrun( -> 1277 options, feed_dict, fetch_list, target_list, run_metadata) 1278

/usr/local/lib/python3.6/dist-packages/tensorflow/python/client/session.py in _call_tf_sessionrun(self, options, feed_dict, fetch_list, target_list, run_metadata) 1366 self._session, options, feed_dict, fetch_list, target_list, -> 1367 run_metadata) 1368

InvalidArgumentError: Cannot batch tensors with different shapes in component 0. First element had shape [32,224,224,3] and element 29 had shape [8,224,224,3]. [[{{node IteratorGetNext_2}} = IteratorGetNextoutput_shapes=[, ], output_types=[DT_FLOAT, DT_FLOAT], _device="/job:localhost/replica:0/task:0/device:CPU:0"]]

During handling of the above exception, another exception occurred:

Please let me know if anyone has any experience with this or know any alternate way.

UPDATE

I was able to solve the problem after using the suggestion by J.E.K.

train_dataset = tf.data.Dataset.from_generator(make_generator,(tf.float32, tf.float32))

However when I give train_dataset to a Keras .fit method I get the following error.

model_regular.fit(train_dataset,steps_per_epoch=1000,epochs=2)

--------------------------------------------------------------------------- ValueError Traceback (most recent call last) in () ----> 1 model_regular.fit(train_dataset,steps_per_epoch=1000,epochs=2)

/usr/local/lib/python3.6/dist-packages/tensorflow/python/keras/engine/training.py in fit(self, x, y, batch_size, epochs, verbose, callbacks, validation_split, validation_data, shuffle, class_weight, sample_weight, initial_epoch, steps_per_epoch, validation_steps, **kwargs) 1507 steps_name='steps_per_epoch', 1508 steps=steps_per_epoch, -> 1509 validation_split=validation_split) 1510 1511 # Prepare validation data.

/usr/local/lib/python3.6/dist-packages/tensorflow/python/keras/engine/training.py in _standardize_user_data(self, x, y, sample_weight, class_weight, batch_size, check_steps, steps_name, steps, validation_split) 948 x = self._dataset_iterator_cache[x] 949 else: --> 950 iterator = x.make_initializable_iterator() 951 self._dataset_iterator_cache[x] = iterator 952 x = iterator

/usr/local/lib/python3.6/dist-packages/tensorflow/python/data/ops/dataset_ops.py in make_initializable_iterator(self, shared_name) 119 with ops.colocate_with(iterator_resource): 120 initializer = gen_dataset_ops.make_iterator(self._as_variant_tensor(), --> 121 iterator_resource) 122 return iterator_ops.Iterator(iterator_resource, initializer, 123 self.output_types, self.output_shapes,

/usr/local/lib/python3.6/dist-packages/tensorflow/python/ops/gen_dataset_ops.py in make_iterator(dataset, iterator, name) 2542 if _ctx is None or not _ctx._eager_context.is_eager: 2543 _, _, _op = _op_def_lib._apply_op_helper( -> 2544 "MakeIterator", dataset=dataset, iterator=iterator, name=name) 2545 return _op 2546 _result = None

/usr/local/lib/python3.6/dist-packages/tensorflow/python/framework/op_def_library.py in _apply_op_helper(self, op_type_name, name, **keywords) 348 # Need to flatten all the arguments into a list. 349 # pylint: disable=protected-access --> 350 g = ops._get_graph_from_inputs(_Flatten(keywords.values())) 351 # pylint: enable=protected-access 352 except AssertionError as e:

/usr/local/lib/python3.6/dist-packages/tensorflow/python/framework/ops.py in _get_graph_from_inputs(op_input_list, graph) 5659 graph = graph_element.graph 5660 elif original_graph_element is not None: -> 5661 _assert_same_graph(original_graph_element, graph_element) 5662 elif graph_element.graph is not graph:
5663 raise ValueError("%s is not from the passed-in graph." % graph_element)

/usr/local/lib/python3.6/dist-packages/tensorflow/python/framework/ops.py in _assert_same_graph(original_item, item) 5595 if original_item.graph is not item.graph: 5596 raise ValueError("%s must be from the same graph as %s." % (item, -> 5597 original_item)) 5598 5599

ValueError: Tensor("IteratorV2:0", shape=(), dtype=resource) must be from the same graph as Tensor("FlatMapDataset:0", shape=(), dtype=variant).

Is this a bug or is Keras fit method not meant to be used this way?

Answer 1

I have tried to reproduce your results with a simple example and I found out that you get different output shapes when one uses batching within the generator function and tf.data.

The Keras function train_datagen.flow_from_directory(batch_size=32) already returns the data with shape [batch_size, width, height, depth]. If one uses tf.data.Dataset().batch(32) the output data is batched again into shape [batch_size, batch_size, width, height, depth].

This could have caused your issue for some reason.