在Keras训练多级图像分类器

Question

我正在学习使用Keras学习训练分类器的教程

https://blog.keras.io/building-powerful-image-classification-models-using-very-little-data.html

具体来说,从作者给出的第二个脚本中,我想将脚本转换为可以训练多类分类器的脚本(是猫和狗的二进制).我的火车文件夹中有5个班级,所以我做了以下更改:

在train_top_model()的功能中:

我变了

model = Sequential()
model.add(Flatten(input_shape=train_data.shape[1:]))
model.add(Dense(256, activation='relu'))
model.add(Dropout(0.5))
model.add(Dense(1, activation='sigmoid'))

model.compile(optimizer='rmsprop', loss='binary_crossentropy', metrics=['accuracy'])

成

model = Sequential()
model.add(Flatten(input_shape=train_data.shape[1:]))
model.add(Dense(256, activation='relu'))
model.add(Dropout(0.5))
model.add(Dense(5, activation='sigmoid'))

model.compile(optimizer='rmsprop', loss='categorical_crossentropy', metrics=['accuracy'])

train_labels = to_categorical(train_labels, 5)
validation_labels = to_categorical(validation_labels, 5)

完成培训后,模型达到了接近99%的训练精度,但仅达到了70%的验证准确度准确度.因此,我开始思考将2课程培训转换为5课程并不是那么简单.也许我在标记类时需要使用单热编码(但我不知道如何)

编辑:

我也附上了我的精细编曲脚本.另一个问题:当微调开始时,准确性没有有效增加.

import os
import h5py
import numpy as np
from keras.preprocessing.image import ImageDataGenerator
from keras import optimizers
from keras.models import Sequential
from keras.layers import Convolution2D, MaxPooling2D, ZeroPadding2D
from keras.layers import Activation, Dropout, Flatten, Dense

# path to the model weights files.
weights_path = 'D:/Users/EJLTZ/Desktop/vgg16_weights.h5'
top_model_weights_path = 'bottleneck_weights_2.h5'
# dimensions of our images.
img_width, img_height = 150, 150

train_data_dir = 'D:/Users/EJLTZ/Desktop/BodyPart-full/train_new'
validation_data_dir = 'D:/Users/EJLTZ/Desktop/BodyPart-full/validation_new'
nb_train_samples = 500
nb_validation_samples = 972
nb_epoch = 50

# build the VGG16 network
model = Sequential()
model.add(ZeroPadding2D((1, 1), input_shape=(3, img_width, img_height)))

model.add(Convolution2D(64, 3, 3, activation='relu', name='conv1_1'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(64, 3, 3, activation='relu', name='conv1_2'))
model.add(MaxPooling2D((2, 2), strides=(2, 2)))

model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(128, 3, 3, activation='relu', name='conv2_1'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(128, 3, 3, activation='relu', name='conv2_2'))
model.add(MaxPooling2D((2, 2), strides=(2, 2)))

model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(256, 3, 3, activation='relu', name='conv3_1'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(256, 3, 3, activation='relu', name='conv3_2'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(256, 3, 3, activation='relu', name='conv3_3'))
model.add(MaxPooling2D((2, 2), strides=(2, 2)))

model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv4_1'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv4_2'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv4_3'))
model.add(MaxPooling2D((2, 2), strides=(2, 2)))

model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv5_1'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv5_2'))
model.add(ZeroPadding2D((1, 1)))
model.add(Convolution2D(512, 3, 3, activation='relu', name='conv5_3'))
model.add(MaxPooling2D((2, 2), strides=(2, 2)))

# load the weights of the VGG16 networks
# (trained on ImageNet, won the ILSVRC competition in 2014)
# note: when there is a complete match between your model definition
# and your weight savefile, you can simply call model.load_weights(filename)
assert os.path.exists(weights_path), 'Model weights not found (see "weights_path" variable in script).'
f = h5py.File(weights_path)
for k in range(f.attrs['nb_layers']):
    if k >= len(model.layers):
        # we don't look at the last (fully-connected) layers in the savefile
        break
    g = f['layer_{}'.format(k)]
    weights = [g['param_{}'.format(p)] for p in range(g.attrs['nb_params'])]
    model.layers[k].set_weights(weights)
f.close()
print('Model loaded.')

# build a classifier model to put on top of the convolutional model
top_model = Sequential()
top_model.add(Flatten(input_shape=model.output_shape[1:]))
top_model.add(Dense(256, activation='relu'))
top_model.add(Dropout(0.5))
top_model.add(Dense(5, activation='softmax'))

# note that it is necessary to start with a fully-trained
# classifier, including the top classifier,
# in order to successfully do fine-tuning
top_model.load_weights(top_model_weights_path)

# add the model on top of the convolutional base
model.add(top_model)

# set the first 25 layers (up to the last conv block)
# to non-trainable (weights will not be updated)
for layer in model.layers[:25]:
    layer.trainable = False

# compile the model with a SGD/momentum optimizer
# and a very slow learning rate.
model.compile(loss='categorical_crossentropy',
          optimizer=optimizers.SGD(lr=1e-4, momentum=0.9),
          metrics=['accuracy'])

# prepare data augmentation configuration
train_datagen = ImageDataGenerator(
    rescale=1./255,
    shear_range=0.2,
    zoom_range=0.2,
    horizontal_flip=True)

test_datagen = ImageDataGenerator(rescale=1./255)

train_generator = train_datagen.flow_from_directory(
    train_data_dir,
    target_size=(img_height, img_width),
    batch_size=32,
    class_mode= 'categorical')

validation_generator = test_datagen.flow_from_directory(
    validation_data_dir,
    target_size=(img_height, img_width),
    batch_size=32,
    class_mode= 'categorical')

# fine-tune the model
model.fit_generator(
    train_generator,
    samples_per_epoch=nb_train_samples,
    nb_epoch=nb_epoch,
    validation_data=validation_generator,
    nb_val_samples=nb_validation_samples)

model.save_weights("fine-tune_weights.h5")
model.save("fine-tune_model.h5", True)

Answer 1

1. 使用softmax作为输出层的激活功能,它是逻辑函数的用于多类情况下的概括.在这里阅读更多相关信息.

2. 如果验证错误远远大于训练误差,就像你的情况一样,它是过度拟合的指标.你应该做一些正则化,它被定义为学习算法的任何变化,旨在减少测试误差而不是训练误差.您可以尝试数据增强,早期停止,噪声注入,更积极的辍学等.

3. 如果你有相同的设置为链接的教程,改变class_mode的train_generator,并validation_generator给categorical它一个将热编码的类.