import tensorflow as tf import keras from keras.layers import Dense, Conv2D, BatchNormalization, Activation from keras.layers import AveragePooling2D, Input, Flatten from keras.regularizers import l2 from keras.models import Model def resnet_layer(inputs, num_filters=16, kernel_size=3, strides=1, activation='relu', batch_normalization=True, conv_first=True): """2D Convolution-Batch Normalization-Activation stack builder # Arguments inputs (tensor): input tensor from input image or previous layer num_filters (int): Conv2D number of filters kernel_size (int): Conv2D square kernel dimensions strides (int): Conv2D square stride dimensions activation (string): activation name batch_normalization (bool): whether to include batch normalization conv_first (bool): conv-bn-activation (True) or activation-bn-conv (False) # Returns x (tensor): tensor as input to the next layer """ conv = Conv2D(num_filters, kernel_size=kernel_size, strides=strides, padding='same', kernel_initializer='he_normal', kernel_regularizer=l2(1e-4)) x = inputs if conv_first: x = conv(x) if batch_normalization: x = BatchNormalization()(x) if activation is not None: x = Activation(activation)(x) else: if batch_normalization: x = BatchNormalization()(x) if activation is not None: x = Activation(activation)(x) x = conv(x) return x def resnet_v1(input_shape, depth, num_classes=10): """ResNet Version 1 Model builder [a] Stacks of 2 x (3 x 3) Conv2D-BN-ReLU Last ReLU is after the shortcut connection. At the beginning of each stage, the feature map size is halved (downsampled) by a convolutional layer with strides=2, while the number of filters is doubled. Within each stage, the layers have the same number filters and the same number of filters. Features maps sizes: stage 0: 32x32, 16 stage 1: 16x16, 32 stage 2: 8x8, 64 The Number of parameters is approx the same as Table 6 of [a]: ResNet20 0.27M ResNet32 0.46M ResNet44 0.66M ResNet56 0.85M ResNet110 1.7M # Arguments input_shape (tensor): shape of input image tensor depth (int): number of core convolutional layers num_classes (int): number of classes (CIFAR10 has 10) # Returns model (Model): Keras model instance """ if (depth - 2) % 6 != 0: raise ValueError('depth should be 6n+2 (eg 20, 32, 44 in [a])') # Start model definition. num_filters = 16 num_res_blocks = int((depth - 2) / 6) inputs = Input(shape=input_shape) x = resnet_layer(inputs=inputs) # Instantiate the stack of residual units for stack in range(3): for res_block in range(num_res_blocks): strides = 1 if stack > 0 and res_block == 0: # first layer but not first stack strides = 2 # downsample y = resnet_layer(inputs=x, num_filters=num_filters, strides=strides) y = resnet_layer(inputs=y, num_filters=num_filters, activation=None) if stack > 0 and res_block == 0: # first layer but not first stack # linear projection residual shortcut connection to match # changed dims x = resnet_layer(inputs=x, num_filters=num_filters, kernel_size=1, strides=strides, activation=None, batch_normalization=False) x = keras.layers.add([x, y]) x = Activation('relu')(x) num_filters *= 2 # Add classifier on top. # v1 does not use BN after last shortcut connection-ReLU x = AveragePooling2D(pool_size=8)(x) y = Flatten()(x) outputs = Dense(num_classes, activation='softmax', kernel_initializer='he_normal')(y) # Instantiate model. model = Model(inputs=inputs, outputs=outputs) return model def resnet_v2(input_shape, depth, num_classes=10): """ResNet Version 2 Model builder [b] Stacks of (1 x 1)-(3 x 3)-(1 x 1) BN-ReLU-Conv2D or also known as bottleneck layer First shortcut connection per layer is 1 x 1 Conv2D. Second and onwards shortcut connection is identity. At the beginning of each stage, the feature map size is halved (downsampled) by a convolutional layer with strides=2, while the number of filter maps is doubled. Within each stage, the layers have the same number filters and the same filter map sizes. Features maps sizes: conv1 : 32x32, 16 stage 0: 32x32, 64 stage 1: 16x16, 128 stage 2: 8x8, 256 # Arguments input_shape (tensor): shape of input image tensor depth (int): number of core convolutional layers num_classes (int): number of classes (CIFAR10 has 10) # Returns model (Model): Keras model instance """ if (depth - 2) % 9 != 0: raise ValueError('depth should be 9n+2 (eg 56 or 110 in [b])') # Start model definition. num_filters_in = 16 num_res_blocks = int((depth - 2) / 9) inputs = Input(shape=input_shape) # v2 performs Conv2D with BN-ReLU on input before splitting into 2 paths x = resnet_layer(inputs=inputs, num_filters=num_filters_in, conv_first=True) # Instantiate the stack of residual units for stage in range(3): for res_block in range(num_res_blocks): activation = 'relu' batch_normalization = True strides = 1 if stage == 0: num_filters_out = num_filters_in * 4 if res_block == 0: # first layer and first stage activation = None batch_normalization = False else: num_filters_out = num_filters_in * 2 if res_block == 0: # first layer but not first stage strides = 2 # downsample # bottleneck residual unit y = resnet_layer(inputs=x, num_filters=num_filters_in, kernel_size=1, strides=strides, activation=activation, batch_normalization=batch_normalization, conv_first=False) y = resnet_layer(inputs=y, num_filters=num_filters_in, conv_first=False) y = resnet_layer(inputs=y, num_filters=num_filters_out, kernel_size=1, conv_first=False) if res_block == 0: # linear projection residual shortcut connection to match # changed dims x = resnet_layer(inputs=x, num_filters=num_filters_out, kernel_size=1, strides=strides, activation=None, batch_normalization=False) x = keras.layers.add([x, y]) num_filters_in = num_filters_out # Add classifier on top. # v2 has BN-ReLU before Pooling x = BatchNormalization()(x) x = Activation('relu')(x) x = AveragePooling2D(pool_size=8)(x) y = Flatten()(x) outputs = Dense(num_classes, activation='softmax', kernel_initializer='he_normal')(y) # Instantiate model. model = Model(inputs=inputs, outputs=outputs) return model