303 lines
14 KiB
Python
303 lines
14 KiB
Python
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# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# ==============================================================================
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"""Contains definitions for the preactivation form of Residual Networks.
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Residual networks (ResNets) were originally proposed in:
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[1] Kaiming He, Xiangyu Zhang, Shaoqing Ren, Jian Sun
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Deep Residual Learning for Image Recognition. arXiv:1512.03385
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The full preactivation 'v2' ResNet variant implemented in this module was
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introduced by:
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[2] Kaiming He, Xiangyu Zhang, Shaoqing Ren, Jian Sun
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Identity Mappings in Deep Residual Networks. arXiv: 1603.05027
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The key difference of the full preactivation 'v2' variant compared to the
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'v1' variant in [1] is the use of batch normalization before every weight layer.
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Another difference is that 'v2' ResNets do not include an activation function in
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the main pathway. Also see [2; Fig. 4e].
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Typical use:
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from tensorflow.contrib.slim.nets import resnet_v2
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ResNet-101 for image classification into 1000 classes:
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# inputs has shape [batch, 224, 224, 3]
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with slim.arg_scope(resnet_v2.resnet_arg_scope()):
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net, end_points = resnet_v2.resnet_v2_101(inputs, 1000, is_training=False)
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ResNet-101 for semantic segmentation into 21 classes:
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# inputs has shape [batch, 513, 513, 3]
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with slim.arg_scope(resnet_v2.resnet_arg_scope(is_training)):
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net, end_points = resnet_v2.resnet_v2_101(inputs,
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21,
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is_training=False,
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global_pool=False,
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output_stride=16)
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"""
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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import tensorflow as tf
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from nets import resnet_utils
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slim = tf.contrib.slim
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resnet_arg_scope = resnet_utils.resnet_arg_scope
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@slim.add_arg_scope
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def bottleneck(inputs, depth, depth_bottleneck, stride, rate=1,
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outputs_collections=None, scope=None):
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"""Bottleneck residual unit variant with BN before convolutions.
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This is the full preactivation residual unit variant proposed in [2]. See
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Fig. 1(b) of [2] for its definition. Note that we use here the bottleneck
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variant which has an extra bottleneck layer.
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When putting together two consecutive ResNet blocks that use this unit, one
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should use stride = 2 in the last unit of the first block.
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Args:
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inputs: A tensor of size [batch, height, width, channels].
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depth: The depth of the ResNet unit output.
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depth_bottleneck: The depth of the bottleneck layers.
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stride: The ResNet unit's stride. Determines the amount of downsampling of
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the units output compared to its input.
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rate: An integer, rate for atrous convolution.
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outputs_collections: Collection to add the ResNet unit output.
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scope: Optional variable_scope.
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Returns:
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The ResNet unit's output.
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"""
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with tf.variable_scope(scope, 'bottleneck_v2', [inputs]) as sc:
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depth_in = slim.utils.last_dimension(inputs.get_shape(), min_rank=4)
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preact = slim.batch_norm(inputs, activation_fn=tf.nn.relu, scope='preact')
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if depth == depth_in:
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shortcut = resnet_utils.subsample(inputs, stride, 'shortcut')
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else:
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shortcut = slim.conv2d(preact, depth, [1, 1], stride=stride,
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normalizer_fn=None, activation_fn=None,
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scope='shortcut')
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residual = slim.conv2d(preact, depth_bottleneck, [1, 1], stride=1,
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scope='conv1')
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residual = resnet_utils.conv2d_same(residual, depth_bottleneck, 3, stride,
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rate=rate, scope='conv2')
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residual = slim.conv2d(residual, depth, [1, 1], stride=1,
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normalizer_fn=None, activation_fn=None,
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scope='conv3')
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output = shortcut + residual
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return slim.utils.collect_named_outputs(outputs_collections,
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sc.original_name_scope,
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output)
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def resnet_v2(inputs,
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blocks,
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num_classes=None,
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is_training=True,
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global_pool=True,
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output_stride=None,
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include_root_block=True,
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reuse=None,
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scope=None):
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"""Generator for v2 (preactivation) ResNet models.
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This function generates a family of ResNet v2 models. See the resnet_v2_*()
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methods for specific model instantiations, obtained by selecting different
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block instantiations that produce ResNets of various depths.
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Training for image classification on Imagenet is usually done with [224, 224]
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inputs, resulting in [7, 7] feature maps at the output of the last ResNet
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block for the ResNets defined in [1] that have nominal stride equal to 32.
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However, for dense prediction tasks we advise that one uses inputs with
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spatial dimensions that are multiples of 32 plus 1, e.g., [321, 321]. In
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this case the feature maps at the ResNet output will have spatial shape
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[(height - 1) / output_stride + 1, (width - 1) / output_stride + 1]
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and corners exactly aligned with the input image corners, which greatly
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facilitates alignment of the features to the image. Using as input [225, 225]
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images results in [8, 8] feature maps at the output of the last ResNet block.
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For dense prediction tasks, the ResNet needs to run in fully-convolutional
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(FCN) mode and global_pool needs to be set to False. The ResNets in [1, 2] all
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have nominal stride equal to 32 and a good choice in FCN mode is to use
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output_stride=16 in order to increase the density of the computed features at
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small computational and memory overhead, cf. http://arxiv.org/abs/1606.00915.
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Args:
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inputs: A tensor of size [batch, height_in, width_in, channels].
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blocks: A list of length equal to the number of ResNet blocks. Each element
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is a resnet_utils.Block object describing the units in the block.
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num_classes: Number of predicted classes for classification tasks. If None
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we return the features before the logit layer.
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is_training: whether is training or not.
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global_pool: If True, we perform global average pooling before computing the
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logits. Set to True for image classification, False for dense prediction.
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output_stride: If None, then the output will be computed at the nominal
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network stride. If output_stride is not None, it specifies the requested
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ratio of input to output spatial resolution.
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include_root_block: If True, include the initial convolution followed by
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max-pooling, if False excludes it. If excluded, `inputs` should be the
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results of an activation-less convolution.
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reuse: whether or not the network and its variables should be reused. To be
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able to reuse 'scope' must be given.
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scope: Optional variable_scope.
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Returns:
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net: A rank-4 tensor of size [batch, height_out, width_out, channels_out].
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If global_pool is False, then height_out and width_out are reduced by a
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factor of output_stride compared to the respective height_in and width_in,
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else both height_out and width_out equal one. If num_classes is None, then
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net is the output of the last ResNet block, potentially after global
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average pooling. If num_classes is not None, net contains the pre-softmax
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activations.
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end_points: A dictionary from components of the network to the corresponding
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activation.
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Raises:
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ValueError: If the target output_stride is not valid.
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"""
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with tf.variable_scope(scope, 'resnet_v2', [inputs], reuse=reuse) as sc:
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end_points_collection = sc.name + '_end_points'
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with slim.arg_scope([slim.conv2d, bottleneck,
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resnet_utils.stack_blocks_dense],
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outputs_collections=end_points_collection):
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with slim.arg_scope([slim.batch_norm], is_training=is_training):
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net = inputs
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if include_root_block:
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if output_stride is not None:
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if output_stride % 4 != 0:
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raise ValueError('The output_stride needs to be a multiple of 4.')
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output_stride /= 4
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# We do not include batch normalization or activation functions in
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# conv1 because the first ResNet unit will perform these. Cf.
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# Appendix of [2].
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with slim.arg_scope([slim.conv2d],
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activation_fn=None, normalizer_fn=None):
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net = resnet_utils.conv2d_same(net, 64, 7, stride=2, scope='conv1')
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net = slim.max_pool2d(net, [3, 3], stride=2, scope='pool1')
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net = resnet_utils.stack_blocks_dense(net, blocks, output_stride)
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# This is needed because the pre-activation variant does not have batch
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# normalization or activation functions in the residual unit output. See
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# Appendix of [2].
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net = slim.batch_norm(net, activation_fn=tf.nn.relu, scope='postnorm')
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if global_pool:
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# Global average pooling.
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net = tf.reduce_mean(net, [1, 2], name='pool5', keep_dims=True)
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if num_classes is not None:
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net = slim.conv2d(net, num_classes, [1, 1], activation_fn=None,
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normalizer_fn=None, scope='logits')
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# Convert end_points_collection into a dictionary of end_points.
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end_points = dict(tf.get_collection(end_points_collection))
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if num_classes is not None:
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end_points['predictions'] = slim.softmax(net, scope='predictions')
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return net, end_points
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resnet_v2.default_image_size = 224
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def resnet_v2_50(inputs,
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num_classes=None,
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is_training=True,
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global_pool=True,
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output_stride=None,
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reuse=None,
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scope='resnet_v2_50'):
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"""ResNet-50 model of [1]. See resnet_v2() for arg and return description."""
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blocks = [
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resnet_utils.Block(
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'block1', bottleneck, [(256, 64, 1)] * 2 + [(256, 64, 2)]),
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resnet_utils.Block(
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'block2', bottleneck, [(512, 128, 1)] * 3 + [(512, 128, 2)]),
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resnet_utils.Block(
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'block3', bottleneck, [(1024, 256, 1)] * 5 + [(1024, 256, 2)]),
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resnet_utils.Block(
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'block4', bottleneck, [(2048, 512, 1)] * 3)]
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return resnet_v2(inputs, blocks, num_classes, is_training=is_training,
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global_pool=global_pool, output_stride=output_stride,
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include_root_block=True, reuse=reuse, scope=scope)
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def resnet_v2_101(inputs,
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num_classes=None,
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is_training=True,
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global_pool=True,
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output_stride=None,
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reuse=None,
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scope='resnet_v2_101'):
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"""ResNet-101 model of [1]. See resnet_v2() for arg and return description."""
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blocks = [
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resnet_utils.Block(
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'block1', bottleneck, [(256, 64, 1)] * 2 + [(256, 64, 2)]),
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resnet_utils.Block(
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'block2', bottleneck, [(512, 128, 1)] * 3 + [(512, 128, 2)]),
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resnet_utils.Block(
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'block3', bottleneck, [(1024, 256, 1)] * 22 + [(1024, 256, 2)]),
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resnet_utils.Block(
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'block4', bottleneck, [(2048, 512, 1)] * 3)]
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return resnet_v2(inputs, blocks, num_classes, is_training=is_training,
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global_pool=global_pool, output_stride=output_stride,
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include_root_block=True, reuse=reuse, scope=scope)
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def resnet_v2_152(inputs,
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num_classes=None,
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is_training=True,
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global_pool=True,
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output_stride=None,
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reuse=None,
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scope='resnet_v2_152'):
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"""ResNet-152 model of [1]. See resnet_v2() for arg and return description."""
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blocks = [
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resnet_utils.Block(
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'block1', bottleneck, [(256, 64, 1)] * 2 + [(256, 64, 2)]),
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resnet_utils.Block(
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'block2', bottleneck, [(512, 128, 1)] * 7 + [(512, 128, 2)]),
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resnet_utils.Block(
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'block3', bottleneck, [(1024, 256, 1)] * 35 + [(1024, 256, 2)]),
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resnet_utils.Block(
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'block4', bottleneck, [(2048, 512, 1)] * 3)]
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return resnet_v2(inputs, blocks, num_classes, is_training=is_training,
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global_pool=global_pool, output_stride=output_stride,
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include_root_block=True, reuse=reuse, scope=scope)
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def resnet_v2_200(inputs,
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num_classes=None,
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is_training=True,
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global_pool=True,
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output_stride=None,
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reuse=None,
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scope='resnet_v2_200'):
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"""ResNet-200 model of [2]. See resnet_v2() for arg and return description."""
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blocks = [
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resnet_utils.Block(
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'block1', bottleneck, [(256, 64, 1)] * 2 + [(256, 64, 2)]),
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resnet_utils.Block(
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'block2', bottleneck, [(512, 128, 1)] * 23 + [(512, 128, 2)]),
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resnet_utils.Block(
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'block3', bottleneck, [(1024, 256, 1)] * 35 + [(1024, 256, 2)]),
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resnet_utils.Block(
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'block4', bottleneck, [(2048, 512, 1)] * 3)]
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return resnet_v2(inputs, blocks, num_classes, is_training=is_training,
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global_pool=global_pool, output_stride=output_stride,
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include_root_block=True, reuse=reuse, scope=scope)
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