TensorFlow (2) CIFAR-10 简单图像识别

coding01

发布于 2021-02-24 11:17:54

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发布于 2021-02-24 11:17:54

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CIFAR-10 图像识别

本文主要学习获取 CIFAR-10 数据集，通过简单的模型对数据集进行训练和识别。

下载数据集

和之前一样，使用 http_proxy 代理：

import matplotlib.pyplot as plt
import tensorflow as tf
from tensorflow.keras import layers, models
import tensorflow_datasets as tfds
import os
import ssl

os.environ['HTTP_PROXY'] = 'http://0.0.0.0:8888'
os.environ['HTTPS_PROXY'] = 'http://0.0.0.0:8888'
ssl._create_default_https_context =  ssl._create_unverified_context

下载 CIFAR-10 数据集[1]：

(x_train, y_train), (x_test, y_test) = tf.keras.datasets.cifar10.load_data()

返回值 Tuple of Numpy arrays: (x_train, y_train), (x_test, y_test). x_train, x_test: uint8 arrays of RGB image data with shape (num_samples, 3, 32, 32) if tf.keras.backend.image_data_format() is 'channels_first', or (num_samples, 32, 32, 3) if the data format is 'channels_last'. y_train, y_test: uint8 arrays of category labels (integers in range 0-9) each with shape (num_samples, 1).

数据集中包含 50000 张 32*32 的彩色图片和这些图相对应的类别标签的训练集，10000 张测试图像。

其中，x_train 是训练集图片，y_train 是对应的标签，x_test 是测试集图片，y_test 是测试集对应的标签。

读取图片

我们将测试集的前 16 张图片和类名打印出来，来确保数据集被正确加载。

class_names = ['airplane', 'automobile', 'bird', 'cat', 'deer',
               'dog', 'frog', 'horse', 'ship', 'truck']

plt.figure(figsize=(10,10))
for i in range(16):
    plt.subplot(4,4,i + 1)
    plt.xticks([])
    plt.yticks([])
    plt.grid(False)
    plt.imshow(x_train[i], cmap=plt.cm.binary)
    # 由于 CIFAR 的标签是 array， 
    # 因此您需要额外的索引（index）。
    plt.xlabel(class_names[train_labels[i][0]])
plt.show()

验证了数据的真确性。下面就开始模式训练和模式测试了。

模式训练

建立模型：

# 将像素的值标准化至0到1的区间内。
x_train, x_test = x_train / 255.0, x_test / 255.0

model = models.Sequential()
model.add(layers.Conv2D(32, (3, 3), activation='relu', input_shape=(32, 32, 3)))
model.add(layers.MaxPooling2D((2, 2)))
model.add(layers.Conv2D(64, (3, 3), activation='relu'))
model.add(layers.MaxPooling2D((2, 2)))
model.add(layers.Conv2D(64, (3, 3), activation='relu'))

model.add(layers.Flatten())
model.add(layers.Dense(64, activation='relu'))
model.add(layers.Dense(10))

model.summary()

Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
conv2d (Conv2D)              (None, 30, 30, 32)        896       
_________________________________________________________________
max_pooling2d (MaxPooling2D) (None, 15, 15, 32)        0         
_________________________________________________________________
conv2d_1 (Conv2D)            (None, 13, 13, 64)        18496     
_________________________________________________________________
max_pooling2d_1 (MaxPooling2 (None, 6, 6, 64)          0         
_________________________________________________________________
conv2d_2 (Conv2D)            (None, 4, 4, 64)          36928     
_________________________________________________________________
flatten (Flatten)            (None, 1024)              0         
_________________________________________________________________
dense (Dense)                (None, 64)                65600     
_________________________________________________________________
dense_1 (Dense)              (None, 10)                650       
=================================================================
Total params: 122,570
Trainable params: 122,570
Non-trainable params: 0
_________________________________________________________________

编译并训练模型：

model.compile(optimizer='adam',
              loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
              metrics=['accuracy'])

history = model.fit(x_train, y_train, epochs=10, 
                    validation_data=(x_test, y_test))

训练过程：

Epoch 1/10
1563/1563 [==============================] - 57s 36ms/step - loss: 1.5198 - accuracy: 0.4505 - val_loss: 1.2727 - val_accuracy: 0.5481
Epoch 2/10
1563/1563 [==============================] - 55s 35ms/step - loss: 1.1464 - accuracy: 0.5947 - val_loss: 1.0817 - val_accuracy: 0.6183
Epoch 3/10
1563/1563 [==============================] - 62s 40ms/step - loss: 0.9908 - accuracy: 0.6552 - val_loss: 0.9716 - val_accuracy: 0.6606
Epoch 4/10
1563/1563 [==============================] - 58s 37ms/step - loss: 0.8882 - accuracy: 0.6899 - val_loss: 0.9284 - val_accuracy: 0.6737
Epoch 5/10
1563/1563 [==============================] - 54s 35ms/step - loss: 0.8148 - accuracy: 0.7145 - val_loss: 0.9531 - val_accuracy: 0.6779
Epoch 6/10
1563/1563 [==============================] - 53s 34ms/step - loss: 0.7595 - accuracy: 0.7333 - val_loss: 0.8891 - val_accuracy: 0.6948
Epoch 7/10
1563/1563 [==============================] - 48s 31ms/step - loss: 0.7137 - accuracy: 0.7508 - val_loss: 0.8636 - val_accuracy: 0.7020
Epoch 8/10
1563/1563 [==============================] - 44s 28ms/step - loss: 0.6681 - accuracy: 0.7656 - val_loss: 0.8790 - val_accuracy: 0.7027
Epoch 9/10
1563/1563 [==============================] - 41s 26ms/step - loss: 0.6332 - accuracy: 0.7779 - val_loss: 0.8627 - val_accuracy: 0.7145
Epoch 10/10
1563/1563 [==============================] - 42s 27ms/step - loss: 0.5896 - accuracy: 0.7920 - val_loss: 0.8551 - val_accuracy: 0.7114

评估模型

plt.plot(history.history['accuracy'], label='accuracy')
plt.plot(history.history['val_accuracy'], label = 'val_accuracy')
plt.xlabel('Epoch')
plt.ylabel('Accuracy')
plt.ylim([0.5, 1])
plt.legend(loc='lower right')
plt.show()

test_loss, test_acc = model.evaluate(x_test, y_test, verbose=2)