Question

在很短的时间内acc和val_acc保持不变之后，我创建了一个模型来对飞机和汽车图像bu进行分类

import numpy as np
import matplotlib as plt
from keras.models import Sequential
from keras.layers import Convolution2D
from keras.layers import MaxPooling2D
from keras.layers import Flatten
from keras.layers import Dense
from keras.preprocessing.image import ImageDataGenerator
from keras.preprocessing.image import image
import os 

model=Sequential()
model.add(Convolution2D(32,(3,3),input_shape=(64,64,3),activation="relu"))
model.add(MaxPooling2D(2,2))
model.add(Convolution2D(64,(3,3),activation="relu"))
model.add(MaxPooling2D(2,2))
model.add(Convolution2D(64,(3,3),activation="sigmoid"))
model.add(MaxPooling2D(2,2))
model.add(Flatten())

model.add(Dense(32,activation="sigmoid"))
model.add(Dense(32,activation="sigmoid"))
model.add(Dense(32,activation="sigmoid"))
model.add(Dense(1,activation="softmax"))
model.compile(optimizer='adam', loss='binary_crossentropy',
               metrics=['accuracy'])
 train_datagen = ImageDataGenerator(
    rescale=1./255,
    shear_range=0.2,
    zoom_range=0.2,
    horizontal_flip=True)

test_datagen = ImageDataGenerator（rescale = 1. / 255）

train_set = train_datagen.flow_from_directory（ 'train_images'， target_size =（64,64）， batch_size = 32， class_mode ='binary'）

test_set = train_datagen.flow_from_directory（ 'val_set'， target_size =（64,64）， batch_size = 32， class_mode ='binary'）

model.fit_generator（动车组， steps_per_epoch = 160， epochs = 25， validation_data = test_set， validation_steps = 40）

Epoch 1/25
30/30 [==============================] - 18s 593ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 2/25
30/30 [==============================] - 15s 491ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 3/25
30/30 [==============================] - 19s 640ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 4/25
30/30 [==============================] - 14s 474ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 5/25
30/30 [==============================] - 16s 532ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 6/25
30/30 [==============================] - 14s 473ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 7/25
30/30 [==============================] - 14s 469ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 8/25
30/30 [==============================] - 14s 469ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 9/25
30/30 [==============================] - 14s 472ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 10/25
30/30 [==============================] - 16s 537ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 11/25
30/30 [==============================] - 18s 590ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 12/25
30/30 [==============================] - 13s 441ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 13/25
30/30 [==============================] - 11s 374ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 14/25
30/30 [==============================] - 11s 370ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 15/25
30/30 [==============================] - 13s 441ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 16/25
30/30 [==============================] - 13s 419ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 17/25
30/30 [==============================] - 12s 401ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 18/25
30/30 [==============================] - 16s 536ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 19/25
30/30 [==============================] - 16s 523ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 20/25
30/30 [==============================] - 16s 530ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 21/25
30/30 [==============================] - 16s 546ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 22/25
30/30 [==============================] - 15s 500ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 23/25
30/30 [==============================] - 16s 546ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 24/25
30/30 [==============================] - 16s 545ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000
Epoch 25/25
30/30 [==============================] - 15s 515ms/step - loss: 7.9712 - acc: 0.5000 - val_loss: 
7.9712 - val_acc: 0.5000

Answer 1

您的模型结构中有几个问题。

首先，对于模型的输出

model.add(Dense(1,activation="softmax"))

您正在使用softmax，这意味着您尝试解决多类分类，而不是二进制分类。如果确实如此，则需要将损失更改为categorical_crossentropy。这样，编译行将变为：

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

如果不是这种情况，并且您只想求解二进制分类，那可能很好，但是我建议将最后一层激活更改为sigmoid

第二个：使用sigmoid作为中间层的激活是一个坏主意，因为它很容易导致梯度消失（更多here）。尝试使用sigmoid更改中间层的所有relu激活，或者使用leakyrelu更改更好的激活

Answer 2

问题就在这里：

model.add(Dense(1,activation="softmax"))

您不能对一个神经元使用softmax，因为它会相对于神经元进行归一化，这意味着对于一个神经元，它将始终产生恒定的1.0值。对于二进制分类，您必须在输出中使用sigmoid激活：

model.add(Dense(1,activation="sigmoid"))

在隐藏层中使用sigmoid激活也是不明智的，因为它们会产生消失的梯度问题。请选择ReLU或类似的激活方式。

在每个时期之后，精度保持恒定

2 个答案: