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densenet.py
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from keras.models import Model
from keras.layers.core import Dense, Dropout, Activation
from keras.layers.convolutional import Convolution2D
from keras.layers.pooling import AveragePooling2D
from keras.layers.pooling import GlobalAveragePooling2D
from keras.layers import Input, merge
from keras.layers.normalization import BatchNormalization
from keras.regularizers import l2
import keras.backend as K
def conv_block(ip, nb_filter, bottleneck=False, dropout_rate=None, weight_decay=1E-4):
''' Apply BatchNorm, Relu 3x3, Conv2D, optional bottleneck block and dropout
Args:
ip: Input keras tensor
nb_filter: number of filters
bottleneck: add bottleneck block
dropout_rate: dropout rate
weight_decay: weight decay factor
Returns: keras tensor with batch_norm, relu and convolution2d added (optional bottleneck)
'''
concat_axis = 1 if K.image_dim_ordering() == "th" else -1
x = BatchNormalization(mode=0, axis=concat_axis, gamma_regularizer=l2(weight_decay),
beta_regularizer=l2(weight_decay))(ip)
x = Activation('relu')(x)
if bottleneck:
inter_channel = nb_filter * 4 # Obtained from https://github.com/liuzhuang13/DenseNet/blob/master/densenet.lua
x = Convolution2D(inter_channel, 1, 1, init='he_uniform', border_mode='same', bias=False,
W_regularizer=l2(weight_decay))(x)
if dropout_rate:
x = Dropout(dropout_rate)(x)
x = BatchNormalization(mode=0, axis=concat_axis, gamma_regularizer=l2(weight_decay),
beta_regularizer=l2(weight_decay))(x)
x = Activation('relu')(x)
x = Convolution2D(nb_filter, 3, 3, init="he_uniform", border_mode="same", bias=False,
W_regularizer=l2(weight_decay))(x)
if dropout_rate:
x = Dropout(dropout_rate)(x)
return x
def transition_block(ip, nb_filter, compression=1.0, dropout_rate=None, weight_decay=1E-4):
''' Apply BatchNorm, Relu 1x1, Conv2D, optional compression, dropout and Maxpooling2D
Args:
ip: keras tensor
nb_filter: number of filters
dropout_rate: dropout rate
weight_decay: weight decay factor
Returns: keras tensor, after applying batch_norm, relu-conv, dropout, maxpool
'''
concat_axis = 1 if K.image_dim_ordering() == "th" else -1
x = BatchNormalization(mode=0, axis=concat_axis, gamma_regularizer=l2(weight_decay),
beta_regularizer=l2(weight_decay))(ip)
x = Activation('relu')(x)
x = Convolution2D(int(nb_filter * compression), 1, 1, init="he_uniform", border_mode="same", bias=False,
W_regularizer=l2(weight_decay))(x)
if dropout_rate:
x = Dropout(dropout_rate)(x)
x = AveragePooling2D((2, 2), strides=(2, 2))(x)
return x
def dense_block(x, nb_layers, nb_filter, growth_rate, bottleneck=False, dropout_rate=None, weight_decay=1E-4):
''' Build a dense_block where the output of each conv_block is fed to subsequent ones
Args:
x: keras tensor
nb_layers: the number of layers of conv_block to append to the model.
nb_filter: number of filters
growth_rate: growth rate
bottleneck: bottleneck block
dropout_rate: dropout rate
weight_decay: weight decay factor
Returns: keras tensor with nb_layers of conv_block appended
'''
concat_axis = 1 if K.image_dim_ordering() == "th" else -1
feature_list = [x]
for i in range(nb_layers):
x = conv_block(x, growth_rate, bottleneck, dropout_rate, weight_decay)
feature_list.append(x)
x = merge(feature_list, mode='concat', concat_axis=concat_axis)
nb_filter += growth_rate
return x, nb_filter
def create_dense_net(nb_classes, img_dim, depth=40, nb_dense_block=3, growth_rate=12, nb_filter=-1,
bottleneck=False, reduction=0.0, dropout_rate=None, weight_decay=1E-4, verbose=True):
''' Build the create_dense_net model
Args:
nb_classes: number of classes
img_dim: tuple of shape (channels, rows, columns) or (rows, columns, channels)
depth: number or layers
nb_dense_block: number of dense blocks to add to end (generally = 3)
growth_rate: number of filters to add per dense block
nb_filter: initial number of filters. Default -1 indicates initial number of filters is 2 * growth_rate
bottleneck: add bottleneck blocks
reduction: reduction factor of transition blocks. Note : reduction value is inverted to compute compression
dropout_rate: dropout rate
weight_decay: weight decay
verbose: print the model type
Returns: keras tensor with nb_layers of conv_block appended
'''
model_input = Input(shape=img_dim)
concat_axis = 1 if K.image_dim_ordering() == "th" else -1
assert (depth - 4) % 3 == 0, "Depth must be 3 N + 4"
if reduction != 0.0:
assert reduction <= 1.0 and reduction > 0.0, "reduction value must lie between 0.0 and 1.0"
# layers in each dense block
nb_layers = int((depth - 4) / 3)
if bottleneck:
nb_layers = int(nb_layers // 2)
# compute initial nb_filter if -1, else accept users initial nb_filter
if nb_filter <= 0:
nb_filter = 2 * growth_rate
# compute compression factor
compression = 1.0 - reduction
# Initial convolution
x = Convolution2D(nb_filter, 3, 3, init="he_uniform", border_mode="same", name="initial_conv2D", bias=False,
W_regularizer=l2(weight_decay))(model_input)
# Add dense blocks
for block_idx in range(nb_dense_block - 1):
x, nb_filter = dense_block(x, nb_layers, nb_filter, growth_rate, bottleneck=bottleneck,
dropout_rate=dropout_rate, weight_decay=weight_decay)
# add transition_block
x = transition_block(x, nb_filter, compression=compression, dropout_rate=dropout_rate,
weight_decay=weight_decay)
nb_filter = int(nb_filter * compression)
# The last dense_block does not have a transition_block
x, nb_filter = dense_block(x, nb_layers, nb_filter, growth_rate, bottleneck=bottleneck,
dropout_rate=dropout_rate, weight_decay=weight_decay)
x = BatchNormalization(mode=0, axis=concat_axis, gamma_regularizer=l2(weight_decay),
beta_regularizer=l2(weight_decay))(x)
x = Activation('relu')(x)
x = GlobalAveragePooling2D()(x)
x = Dense(nb_classes, activation='softmax', W_regularizer=l2(weight_decay), b_regularizer=l2(weight_decay))(x)
densenet = Model(input=model_input, output=x, name="create_dense_net")
if verbose:
if bottleneck and not reduction:
print("Bottleneck DenseNet-B-%d-%d created." % (depth, growth_rate))
elif not bottleneck and reduction > 0.0:
print("DenseNet-C-%d-%d with %0.1f compression created." % (depth, growth_rate, compression))
elif bottleneck and reduction > 0.0:
print("Bottleneck DenseNet-BC-%d-%d with %0.1f compression created." % (depth, growth_rate, compression))
else:
print("DenseNet-%d-%d created." % (depth, growth_rate))
return densenet
if __name__ == '__main__':
model = create_dense_net(nb_classes=10, img_dim=(3, 32, 32), depth=40, growth_rate=12, bottleneck=True, reduction=0.5)
model.summary()