# 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. # ============================================================================== """ResNet50 model for Keras. Adapted from tf.keras.applications.resnet50.ResNet50(). This is ResNet model version 1.5. Related papers/blogs: - https://arxiv.org/abs/1512.03385 - https://arxiv.org/pdf/1603.05027v2.pdf - http://torch.ch/blog/2016/02/04/resnets.html """ from __future__ import absolute_import from __future__ import division from __future__ import print_function import os import warnings from tensorflow.python.keras import backend from tensorflow.python.keras import layers from tensorflow.python.keras import models from tensorflow.python.keras import regularizers from tensorflow.python.keras import utils L2_WEIGHT_DECAY = 1e-4 BATCH_NORM_DECAY = 0.9 BATCH_NORM_EPSILON = 1e-5 def identity_block(input_tensor, kernel_size, filters, stage, block): """The identity block is the block that has no conv layer at shortcut. # Arguments input_tensor: input tensor kernel_size: default 3, the kernel size of middle conv layer at main path filters: list of integers, the filters of 3 conv layer at main path stage: integer, current stage label, used for generating layer names block: 'a','b'..., current block label, used for generating layer names # Returns Output tensor for the block. """ filters1, filters2, filters3 = filters if backend.image_data_format() == 'channels_last': bn_axis = 3 else: bn_axis = 1 conv_name_base = 'res' + str(stage) + block + '_branch' bn_name_base = 'bn' + str(stage) + block + '_branch' x = layers.Conv2D(filters1, (1, 1), use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2a')(input_tensor) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2a')(x) x = layers.Activation('relu')(x) x = layers.Conv2D(filters2, kernel_size, padding='same', use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2b')(x) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2b')(x) x = layers.Activation('relu')(x) x = layers.Conv2D(filters3, (1, 1), use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2c')(x) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2c')(x) x = layers.add([x, input_tensor]) x = layers.Activation('relu')(x) return x def conv_block(input_tensor, kernel_size, filters, stage, block, strides=(2, 2)): """A block that has a conv layer at shortcut. # Arguments input_tensor: input tensor kernel_size: default 3, the kernel size of middle conv layer at main path filters: list of integers, the filters of 3 conv layer at main path stage: integer, current stage label, used for generating layer names block: 'a','b'..., current block label, used for generating layer names strides: Strides for the second conv layer in the block. # Returns Output tensor for the block. Note that from stage 3, the second conv layer at main path is with strides=(2, 2) And the shortcut should have strides=(2, 2) as well """ filters1, filters2, filters3 = filters if backend.image_data_format() == 'channels_last': bn_axis = 3 else: bn_axis = 1 conv_name_base = 'res' + str(stage) + block + '_branch' bn_name_base = 'bn' + str(stage) + block + '_branch' x = layers.Conv2D(filters1, (1, 1), use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2a')(input_tensor) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2a')(x) x = layers.Activation('relu')(x) x = layers.Conv2D(filters2, kernel_size, strides=strides, padding='same', use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2b')(x) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2b')(x) x = layers.Activation('relu')(x) x = layers.Conv2D(filters3, (1, 1), use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '2c')(x) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '2c')(x) shortcut = layers.Conv2D(filters3, (1, 1), strides=strides, use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name=conv_name_base + '1')(input_tensor) shortcut = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name=bn_name_base + '1')(shortcut) x = layers.add([x, shortcut]) x = layers.Activation('relu')(x) return x def resnet50(num_classes): # TODO(tfboyd): add training argument, just lik resnet56. """Instantiates the ResNet50 architecture. Args: num_classes: `int` number of classes for image classification. Returns: A Keras model instance. """ input_shape = (224, 224, 3) img_input = layers.Input(shape=input_shape) if backend.image_data_format() == 'channels_first': x = layers.Lambda(lambda x: backend.permute_dimensions(x, (0, 3, 1, 2)), name='transpose')(img_input) bn_axis = 1 else: # channels_last x = img_input bn_axis = 3 x = layers.ZeroPadding2D(padding=(3, 3), name='conv1_pad')(x) x = layers.Conv2D(64, (7, 7), strides=(2, 2), padding='valid', use_bias=False, kernel_initializer='he_normal', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name='conv1')(x) x = layers.BatchNormalization(axis=bn_axis, momentum=BATCH_NORM_DECAY, epsilon=BATCH_NORM_EPSILON, name='bn_conv1')(x) x = layers.Activation('relu')(x) x = layers.ZeroPadding2D(padding=(1, 1), name='pool1_pad')(x) x = layers.MaxPooling2D((3, 3), strides=(2, 2))(x) x = conv_block(x, 3, [64, 64, 256], stage=2, block='a', strides=(1, 1)) x = identity_block(x, 3, [64, 64, 256], stage=2, block='b') x = identity_block(x, 3, [64, 64, 256], stage=2, block='c') x = conv_block(x, 3, [128, 128, 512], stage=3, block='a') x = identity_block(x, 3, [128, 128, 512], stage=3, block='b') x = identity_block(x, 3, [128, 128, 512], stage=3, block='c') x = identity_block(x, 3, [128, 128, 512], stage=3, block='d') x = conv_block(x, 3, [256, 256, 1024], stage=4, block='a') x = identity_block(x, 3, [256, 256, 1024], stage=4, block='b') x = identity_block(x, 3, [256, 256, 1024], stage=4, block='c') x = identity_block(x, 3, [256, 256, 1024], stage=4, block='d') x = identity_block(x, 3, [256, 256, 1024], stage=4, block='e') x = identity_block(x, 3, [256, 256, 1024], stage=4, block='f') x = conv_block(x, 3, [512, 512, 2048], stage=5, block='a') x = identity_block(x, 3, [512, 512, 2048], stage=5, block='b') x = identity_block(x, 3, [512, 512, 2048], stage=5, block='c') x = layers.GlobalAveragePooling2D(name='avg_pool')(x) x = layers.Dense( num_classes, activation='softmax', kernel_regularizer=regularizers.l2(L2_WEIGHT_DECAY), bias_regularizer=regularizers.l2(L2_WEIGHT_DECAY), name='fc1000')(x) # Create model. return models.Model(img_input, x, name='resnet50')