Adds FreezableSyncBatchNormalization to the Object Detection API.

PiperOrigin-RevId: 352601466

research/object_detection/builders/hyperparams_builder.py

@@ -20,7 +20,11 @@ import tf_slim as slim
 from object_detection.core import freezable_batch_norm
 from object_detection.protos import hyperparams_pb2
 from object_detection.utils import context_manager
+from object_detection.utils import tf_version
 
+# pylint: disable=g-import-not-at-top
+if tf_version.is_tf2():
+  from object_detection.core import freezable_sync_batch_norm
 # pylint: enable=g-import-not-at-top
 
 
@@ -60,9 +64,14 @@ class KerasLayerHyperparams(object):
                        'hyperparams_pb.Hyperparams.')
 
     self._batch_norm_params = None
+    self._use_sync_batch_norm = False
     if hyperparams_config.HasField('batch_norm'):
       self._batch_norm_params = _build_keras_batch_norm_params(
           hyperparams_config.batch_norm)
+    elif hyperparams_config.HasField('sync_batch_norm'):
+      self._use_sync_batch_norm = True
+      self._batch_norm_params = _build_keras_batch_norm_params(
+          hyperparams_config.sync_batch_norm)
 
     self._force_use_bias = hyperparams_config.force_use_bias
     self._activation_fn = _build_activation_fn(hyperparams_config.activation)
@@ -133,10 +142,12 @@ class KerasLayerHyperparams(object):
       is False)
     """
     if self.use_batch_norm():
+      if self._use_sync_batch_norm:
+        return freezable_sync_batch_norm.FreezableSyncBatchNorm(
+            training=training, **self.batch_norm_params(**overrides))
+      else:
         return freezable_batch_norm.FreezableBatchNorm(
-          training=training,
-          **self.batch_norm_params(**overrides)
-      )
+            training=training, **self.batch_norm_params(**overrides))
     else:
       return tf.keras.layers.Lambda(tf.identity)
 
@@ -219,6 +230,10 @@ def build(hyperparams_config, is_training):
     raise ValueError('Hyperparams force_use_bias only supported by '
                      'KerasLayerHyperparams.')
 
+  if hyperparams_config.HasField('sync_batch_norm'):
+    raise ValueError('Hyperparams sync_batch_norm only supported by '
+                     'KerasLayerHyperparams.')
+
   normalizer_fn = None
   batch_norm_params = None
   if hyperparams_config.HasField('batch_norm'):

research/object_detection/core/freezable_batch_norm_tf2_test.py

@@ -17,25 +17,40 @@
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
+
 import unittest
+
+from absl.testing import parameterized
 import numpy as np
 from six.moves import zip
-import tensorflow.compat.v1 as tf
+import tensorflow as tf
 
 
 from object_detection.core import freezable_batch_norm
 from object_detection.utils import tf_version
 
+# pylint: disable=g-import-not-at-top
+if tf_version.is_tf2():
+  from object_detection.core import freezable_sync_batch_norm
+# pylint: enable=g-import-not-at-top
+
 
 @unittest.skipIf(tf_version.is_tf1(), 'Skipping TF2.X only test.')
-class FreezableBatchNormTest(tf.test.TestCase):
+class FreezableBatchNormTest(tf.test.TestCase, parameterized.TestCase):
   """Tests for FreezableBatchNorm operations."""
 
-  def _build_model(self, training=None):
+  def _build_model(self, use_sync_batch_norm, training=None):
     model = tf.keras.models.Sequential()
+    norm = None
+    if use_sync_batch_norm:
+      norm = freezable_sync_batch_norm.FreezableSyncBatchNorm(training=training,
+                                                              input_shape=(10,),
+                                                              momentum=0.8)
+    else:
       norm = freezable_batch_norm.FreezableBatchNorm(training=training,
                                                      input_shape=(10,),
                                                      momentum=0.8)
+
     model.add(norm)
     return model, norm
 
@@ -43,8 +58,9 @@ class FreezableBatchNormTest(tf.test.TestCase):
     for source, target in zip(source_weights, target_weights):
       target.assign(source)
 
-  def _train_freezable_batch_norm(self, training_mean, training_var):
-    model, _ = self._build_model()
+  def _train_freezable_batch_norm(self, training_mean, training_var,
+                                  use_sync_batch_norm):
+    model, _ = self._build_model(use_sync_batch_norm=use_sync_batch_norm)
     model.compile(loss='mse', optimizer='sgd')
 
     # centered on training_mean, variance training_var
@@ -72,7 +88,8 @@ class FreezableBatchNormTest(tf.test.TestCase):
     np.testing.assert_allclose(out.numpy().mean(), 0.0, atol=1.5e-1)
     np.testing.assert_allclose(out.numpy().std(), 1.0, atol=1.5e-1)
 
-  def test_batchnorm_freezing_training_none(self):
+  @parameterized.parameters(True, False)
+  def test_batchnorm_freezing_training_none(self, use_sync_batch_norm):
     training_mean = 5.0
     training_var = 10.0
 
@@ -81,12 +98,13 @@ class FreezableBatchNormTest(tf.test.TestCase):
 
     # Initially train the batch norm, and save the weights
     trained_weights = self._train_freezable_batch_norm(training_mean,
-                                                       training_var)
+                                                       training_var,
+                                                       use_sync_batch_norm)
 
     # Load the batch norm weights, freezing training to True.
     # Apply the batch norm layer to testing data and ensure it is normalized
     # according to the batch statistics.
-    model, norm = self._build_model(training=True)
+    model, norm = self._build_model(use_sync_batch_norm, training=True)
     self._copy_weights(trained_weights, model.weights)
 
     # centered on testing_mean, variance testing_var
@@ -136,7 +154,8 @@ class FreezableBatchNormTest(tf.test.TestCase):
                                testing_mean, testing_var, training_arg,
                                training_mean, training_var)
 
-  def test_batchnorm_freezing_training_false(self):
+  @parameterized.parameters(True, False)
+  def test_batchnorm_freezing_training_false(self, use_sync_batch_norm):
     training_mean = 5.0
     training_var = 10.0
 
@@ -145,12 +164,13 @@ class FreezableBatchNormTest(tf.test.TestCase):
 
     # Initially train the batch norm, and save the weights
     trained_weights = self._train_freezable_batch_norm(training_mean,
-                                                       training_var)
+                                                       training_var,
+                                                       use_sync_batch_norm)
 
     # Load the batch norm back up, freezing training to False.
     # Apply the batch norm layer to testing data and ensure it is normalized
     # according to the training data's statistics.
-    model, norm = self._build_model(training=False)
+    model, norm = self._build_model(use_sync_batch_norm, training=False)
     self._copy_weights(trained_weights, model.weights)
 
     # centered on testing_mean, variance testing_var

research/object_detection/core/freezable_sync_batch_norm.py

+# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+
+"""A freezable batch norm layer that uses Keras sync batch normalization."""
+import tensorflow as tf
+
+
+class FreezableSyncBatchNorm(tf.keras.layers.experimental.SyncBatchNormalization
+                            ):
+  """Sync Batch normalization layer (Ioffe and Szegedy, 2014).
+
+  This is a `freezable` batch norm layer that supports setting the `training`
+  parameter in the __init__ method rather than having to set it either via
+  the Keras learning phase or via the `call` method parameter. This layer will
+  forward all other parameters to the Keras `SyncBatchNormalization` layer
+
+  This is class is necessary because Object Detection model training sometimes
+  requires batch normalization layers to be `frozen` and used as if it was
+  evaluation time, despite still training (and potentially using dropout layers)
+
+  Like the default Keras SyncBatchNormalization layer, this will normalize the
+  activations of the previous layer at each batch,
+  i.e. applies a transformation that maintains the mean activation
+  close to 0 and the activation standard deviation close to 1.
+
+  Input shape:
+      Arbitrary. Use the keyword argument `input_shape`
+      (tuple of integers, does not include the samples axis)
+      when using this layer as the first layer in a model.
+
+  Output shape:
+      Same shape as input.
+
+  References:
+      - [Batch Normalization: Accelerating Deep Network Training by Reducing
+        Internal Covariate Shift](https://arxiv.org/abs/1502.03167)
+  """
+
+  def __init__(self, training=None, **kwargs):
+    """Constructor.
+
+    Args:
+      training: If False, the layer will normalize using the moving average and
+        std. dev, without updating the learned avg and std. dev.
+        If None or True, the layer will follow the keras SyncBatchNormalization
+        layer strategy of checking the Keras learning phase at `call` time to
+        decide what to do.
+      **kwargs: The keyword arguments to forward to the keras
+        SyncBatchNormalization layer constructor.
+    """
+    super(FreezableSyncBatchNorm, self).__init__(**kwargs)
+    self._training = training
+
+  def call(self, inputs, training=None):
+    # Override the call arg only if the batchnorm is frozen. (Ignore None)
+    if self._training is False:  # pylint: disable=g-bool-id-comparison
+      training = self._training
+    return super(FreezableSyncBatchNorm, self).call(inputs, training=training)

research/object_detection/protos/hyperparams.proto

@@ -42,6 +42,8 @@ message Hyperparams {
     // Note that if nothing below is selected, then no normalization is applied
     // BatchNorm hyperparameters.
     BatchNorm batch_norm = 5;
+    // SyncBatchNorm hyperparameters (KerasLayerHyperparams only).
+    BatchNorm sync_batch_norm = 9;
     // GroupNorm hyperparameters. This is only supported on a subset of models.
     // Note that the current implementation of group norm instantiated in
     // tf.contrib.group.layers.group_norm() only supports fixed_size_resizer