draft for faster rcnn resnet vi fpn feature extractor

research/object_detection/models/faster_rcnn_resnet_v1_fpn_keras_feature_extractor.py

-"""Faster RCNN Keras-based Resnet v1 FPN Feature Extractor."""
+# Copyright 2020 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.
+# ==============================================================================
+
+"""Faster RCNN Keras-based Resnet V1 FPN Feature Extractor."""
+
+import tensorflow.compat.v1 as tf
 
 from object_detection.meta_architectures import faster_rcnn_meta_arch
 from object_detection.models import feature_map_generators
 from object_detection.models.keras_models import resnet_v1
 from object_detection.models.keras_models import model_utils
 from object_detection.utils import ops
+from object_detection.utils import shape_utils
 
+_RESNET_MODEL_OUTPUT_LAYERS = {
+    'resnet_v1_50': ['conv2_block3_out', 'conv3_block4_out',
+                     'conv4_block6_out', 'conv5_block3_out'],
+    'resnet_v1_101': ['conv2_block3_out', 'conv3_block4_out',
+                      'conv4_block23_out', 'conv5_block3_out'],
+    'resnet_v1_152': ['conv2_block3_out', 'conv3_block8_out',
+                      'conv4_block36_out', 'conv5_block3_out'],
+}
 
-class FasterRCNNFPNKerasFeatureExtractor(
-    faster_rcnn_meta_arch.FasterRCNNKerasFeatureExtractor):
-  """Faster RCNN Feature Extractor using Keras-based Resnet v1  FPN features."""
 
-  def __init__(self, ...):
-    # TODO: constructor
-    pass
+class FasterRCNNResnetV1FPNKerasFeatureExtractor(
+    faster_rcnn_meta_arch.FasterRCNNFeatureExtractor):
+  """Faster RCNN Feature Extractor using Keras-based Resnet V1 FPN features."""
 
-  def build(self, ...):
-    # TODO: Build the structure, should be very similar as ssd_*_fpn_keras_feature_extractor.py
-    # ResNet-101 (object_detection.models.keras_models)
-    # object_detection.models.feature_map_generators
-    pass
-  
-  def preprocess(self, ...):
-    # TODO: should be the same as others
-    pass
-  
-  def _extract_proposal_features(self, ...):
-    # TODO: Extracts first stage RPN features
-    # Fpn_feature_levels 
-    pass
-  
-  def _extract_box_classifier_features(self, ...):
-    # TODO: Extracts second stage box classifier features.
-    pass
+  def __init__(self,
+               is_training,
+               first_stage_features_stride,
+               conv_hyperparams,
+               min_depth,
+               depth_multiplier,
+               resnet_v1_base_model,
+               resnet_v1_base_model_name,
+               batch_norm_trainable=False,
+               weight_decay=0.0,
+               fpn_min_level=3,
+               fpn_max_level=7,
+               additional_layer_depth=256,
+               override_base_feature_extractor_hyperparams=False):
+    # FIXME: fix doc string for fpn min level and fpn max level
+    """Constructor.
+
+    Args:
+      is_training: See base class.
+      first_stage_features_stride: See base class.
+
+      conv_hyperparameters: a `hyperparams_builder.KerasLayerHyperparams` object
+        containing convolution hyperparameters for the layers added on top of
+        the base feature extractor.
+      min_depth: Minimum number of filters in the convolutional layers.
+      depth_multiplier: The depth multiplier to modify the number of filters
+        in the convolutional layers.
+      resnet_v1_base_model: base resnet v1 network to use. One of
+        the resnet_v1.resnet_v1_{50,101,152} models.
+      resnet_v1_base_model_name: model name under which to construct resnet v1.
+
+      batch_norm_trainable: See base class.
+      weight_decay: See base class.
+
+      fpn_min_level: the highest resolution feature map to use in FPN. The valid
+        values are {2, 3, 4, 5} which map to MobileNet v1 layers
+        {Conv2d_3_pointwise, Conv2d_5_pointwise, Conv2d_11_pointwise,
+        Conv2d_13_pointwise}, respectively.
+      fpn_max_level: the smallest resolution feature map to construct or use in
+        FPN. FPN constructions uses features maps starting from fpn_min_level
+        upto the fpn_max_level. In the case that there are not enough feature
+        maps in the backbone network, additional feature maps are created by
+        applying stride 2 convolutions until we get the desired number of fpn
+        levels.
+      additional_layer_depth: additional feature map layer channel depth.
+      override_base_feature_extractor_hyperparams: Whether to override
+        hyperparameters of the base feature extractor with the one from
+        `conv_hyperparams`.
+
+    Raises:
+
+    """
+    super(FasterRCNNResnetV1FPNKerasFeatureExtractor, self).__init__(
+          is_training=is_training,
+          first_stage_features_stride=first_stage_features_stride,
+          batch_norm_trainable=batch_norm_trainable,
+          weight_decay=weight_decay)
+    self._conv_hyperparams = conv_hyperparams
+    self._min_depth = min_depth
+    self._depth_multiplier = depth_multiplier
+    self._additional_layer_depth = additional_layer_depth
+    self._freeze_batchnorm = (not batch_norm_trainable)
+    self._override_base_feature_extractor_hyperparams = 
+                    override_base_feature_extractor_hyperparams
+    self._fpn_min_level = fpn_min_level
+    self._fpn_max_level = fpn_max_level
+    self._resnet_v1_base_model = resnet_v1_base_model
+    self._resnet_v1_base_model_name = resnet_v1_base_model_name
+    self._resnet_block_names = ['block1', 'block2', 'block3', 'block4']
+    self.classification_backbone = None
+    self._fpn_features_generator = None
+    self._coarse_feature_layers = []
+
+  def build(self,):
+    # TODO: Refine doc string
+    """Build Resnet V1 FPN architecture."""
+    full_resnet_v1_model = self._resnet_v1_base_model(
+        batchnorm_training=self._train_batch_norm,
+        conv_hyperparams=(self._conv_hyperparams
+                          if self._override_base_feature_extractor_hyperparams
+                          else None),
+        min_depth=self._min_depth,
+        depth_multiplier=self._depth_multiplier,
+        classes=None,
+        weights=None,
+        include_top=False)
+    output_layers = _RESNET_MODEL_OUTPUT_LAYERS[self._resnet_v1_base_model_name]
+    outputs = [full_resnet_v1_model.get_layer(output_layer_name).output
+               for output_layer_name in output_layers]
+    self.classification_backbone = tf.keras.Model(
+        inputs=full_resnet_v1_model.inputs,
+        outputs=outputs)
+    self._depth_fn = lambda d: max(
+        int(d * self._depth_multiplier), self._min_depth)
+    self._base_fpn_max_level = min(self._fpn_max_level, 5)
+    self._num_levels = self._base_fpn_max_level + 1 - self._fpn_min_level
+    self._fpn_features_generator = (
+        feature_map_generators.KerasFpnTopDownFeatureMaps(
+            num_levels=self._num_levels,
+            depth=self._depth_fn(self._additional_layer_depth),
+            is_training=self._is_training,
+            conv_hyperparams=self._conv_hyperparams,
+            freeze_batchnorm=self._freeze_batchnorm,
+            name='FeatureMaps'))
+    # Construct coarse feature layers
+    depth = self._depth_fn(self._additional_layer_depth)
+    for i in range(self._base_fpn_max_level, self._fpn_max_level):
+      layers = []
+      layer_name = 'bottom_up_block{}'.format(i)
+      layers.append(
+          tf.keras.layers.Conv2D(
+              depth,
+              [3, 3],
+              padding='SAME',
+              strides=2,
+              name=layer_name + '_conv',
+              **self._conv_hyperparams.params()))
+      layers.append(
+          self._conv_hyperparams.build_batch_norm(
+              training=(self._is_training and not self._freeze_batchnorm),
+              name=layer_name + '_batchnorm'))
+      layers.append(
+          self._conv_hyperparams.build_activation_layer(
+              name=layer_name))
+      self._coarse_feature_layers.append(layers)
+    self.built = True
+
+  def preprocess(self, resized_inputs):
+    """Faster R-CNN Resnet V1 preprocessing.
+
+    VGG style channel mean subtraction as described here:
+    https://gist.github.com/ksimonyan/211839e770f7b538e2d8#file-readme-md
+    Note that if the number of channels is not equal to 3, the mean subtraction
+    will be skipped and the original resized_inputs will be returned.
+
+    Args:
+      resized_inputs: A [batch, height_in, width_in, channels] float32 tensor
+        representing a batch of images with values between 0 and 255.0.
+
+    Returns:
+      preprocessed_inputs: A [batch, height_out, width_out, channels] float32
+        tensor representing a batch of images.
+
+    """
+    if resized_inputs.shape.as_list()[3] == 3:
+      channel_means = [123.68, 116.779, 103.939]
+      return resized_inputs - [[channel_means]]
+    else:
+      return resized_inputs
   
-  def restore_from_classification_checkpoint_fn(self, ...):
-    # follow the none fpn version
-    pass
+  def _extract_proposal_features(self, preprocessed_inputs, scope=None):
+    # TODO: doc string
+    """"""
+    preprocessed_inputs = shape_utils.check_min_image_dim(
+        129, preprocessed_inputs)
+
+    with tf.name_scope(scope):
+      with tf.name_scope('ResnetV1FPN'):
+        image_features = self.classification_backbone(preprocessed_inputs)
+
+        feature_block_list = []
+        for level in range(self._fpn_min_level, self._base_fpn_max_level + 1):
+          feature_block_list.append('block{}'.format(level - 1))
+        feature_block_map = dict(
+            list(zip(self._resnet_block_names, image_features)))
+        fpn_input_image_features = [
+            (feature_block, feature_block_map[feature_block])
+            for feature_block in feature_block_list]
+        fpn_features = self._fpn_features_generator(fpn_input_image_features)
+
+        return fpn_features
+        
+
+  def _extract_box_classifier_features(self, proposal_feature_maps, scope=None):
+    with tf.name_scope(scope):
+      with tf.name_scope('ResnetV1FPN'):
+        feature_maps = []
+        for level in range(self._fpn_min_level, self._base_fpn_max_level + 1):
+          feature_maps.append(proposal_feature_maps['top_down_block{}'.format(level-1)])
+        self.last_feature_map = proposal_feature_maps['top_down_block{}'.format(
+            self._base_fpn_max_level - 1)]
+
+        for coarse_feature_layers in self._coarse_feature_layers:
+          for layer in coarse_feature_layers:
+            last_feature_map = layer(last_feature_map)
+          feature_maps.append(self.last_feature_map)
+
+        return feature_maps
+