squeezenet.py

import numpy as np
import keras
from keras.models import Model
from keras.layers import Input, Convolution2D, MaxPooling2D
from keras.layers import Activation, Dropout, GlobalAveragePooling2D, concatenate


mean = np.array([0.485, 0.456, 0.406], dtype='float32')
std = np.array([0.229, 0.224, 0.225], dtype='float32')


def preprocess_input(x):
    x /= 255.0
    x -= mean
    x /= std
    return x


# a building block of the SqueezeNet architecture
def fire_module(number, x, squeeze, expand, weight_decay=None, trainable=False):
    
    module_name = 'fire' + number
    
    if trainable and weight_decay is not None:
        kernel_regularizer = keras.regularizers.l2(weight_decay) 
    else:
        kernel_regularizer = None
    
    x = Convolution2D(
        squeeze, (1, 1), 
        name=module_name + '/' + 'squeeze',
        trainable=trainable, 
        kernel_regularizer=kernel_regularizer
    )(x)
    x = Activation('relu')(x)

    a = Convolution2D(
        expand, (1, 1),
        name=module_name + '/' + 'expand1x1',
        trainable=trainable, 
        kernel_regularizer=kernel_regularizer
    )(x)
    a = Activation('relu')(a)

    b = Convolution2D(
        expand, (3, 3), padding='same',
        name=module_name + '/' + 'expand3x3',
        trainable=trainable, 
        kernel_regularizer=kernel_regularizer
    )(x)
    b = Activation('relu')(b)

    return concatenate([a, b])


def SqueezeNet(weight_decay, image_size=224):

    image = Input(shape=(image_size, image_size, 3))

    x = Convolution2D(
        64, (3, 3), strides=(2, 2), name='conv1', 
        trainable=False
    )(image) # 111, 111, 64
    
    x = Activation('relu')(x)
    x = MaxPooling2D(pool_size=(3, 3), strides=(2, 2))(x) # 55, 55, 64

    x = fire_module('2', x, squeeze=16, expand=64) # 55, 55, 128
    x = fire_module('3', x, squeeze=16, expand=64) # 55, 55, 128
    x = MaxPooling2D(pool_size=(3, 3), strides=(2, 2))(x) # 27, 27, 128

    x = fire_module('4', x, squeeze=32, expand=128) # 27, 27, 256
    x = fire_module('5', x, squeeze=32, expand=128) # 27, 27, 256
    x = MaxPooling2D(pool_size=(3, 3), strides=(2, 2))(x) # 13, 13, 256
    
    x = fire_module('6', x, squeeze=48, expand=192) # 13, 13, 384
    x = fire_module('7', x, squeeze=48, expand=192) # 13, 13, 384
    x = fire_module('8', x, squeeze=64, expand=256) # 13, 13, 512
    x = fire_module('9', x, squeeze=64, expand=256) # 13, 13, 512
    
    x = Dropout(0.5)(x)
    x = Convolution2D(
        256, (1, 1), name='conv10',
        kernel_initializer=keras.initializers.RandomNormal(stddev=0.01),
        kernel_regularizer=keras.regularizers.l2(weight_decay)
    )(x) # 13, 13, 256
    
    x = Activation('relu')(x)
    logits = GlobalAveragePooling2D()(x) # 256
    probabilities = Activation('softmax')(logits)
    
    model = Model(image, probabilities)
    model.load_weights('squeezenet_weights.hdf5', by_name=True)
    
    return model