Copyright 2019 The TensorFlow Authors.
Convolutional Neural Network (CNN)#
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This tutorial demonstrates training a simple Convolutional Neural Network (CNN) to classify CIFAR images. Because this tutorial uses the Keras Sequential API, creating and training your model will take just a few lines of code.
import tensorflow as tf from tensorflow.keras import datasets, layers, models import matplotlib.pyplot as plt
Download and prepare the CIFAR10 dataset#
The CIFAR10 dataset contains 60,000 color images in 10 classes, with 6,000 images in each class. The dataset is divided into 50,000 training images and 10,000 testing images. The classes are mutually exclusive and there is no overlap between them.
(train_images, train_labels), (test_images, test_labels) = datasets.cifar10.load_data() # Normalize pixel values to be between 0 and 1 train_images, test_images = train_images / 255.0, test_images / 255.0
Downloading data from https://www.cs.toronto.edu/~kriz/cifar-10-python.tar.gz 170500096/170498071 [==============================] - 6s 0us/step 170508288/170498071 [==============================] - 6s 0us/step
Verify the data#
To verify that the dataset looks correct, let’s plot the first 25 images from the training set and display the class name below each image:
class_names = ['airplane', 'automobile', 'bird', 'cat', 'deer', 'dog', 'frog', 'horse', 'ship', 'truck'] plt.figure(figsize=(10,10)) for i in range(25): plt.subplot(5,5,i+1) plt.xticks() plt.yticks() plt.grid(False) plt.imshow(train_images[i]) # The CIFAR labels happen to be arrays, # which is why you need the extra index plt.xlabel(class_names[train_labels[i]]) plt.show()
Create the convolutional base#
As input, a CNN takes tensors of shape (image_height, image_width, color_channels), ignoring the batch size. If you are new to these dimensions, color_channels refers to (R,G,B). In this example, you will configure your CNN to process inputs of shape (32, 32, 3), which is the format of CIFAR images. You can do this by passing the argument
input_shape to your first layer.
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'))
2022-03-05 17:16:04.861954: I tensorflow/core/platform/cpu_feature_guard.cc:151] This TensorFlow binary is optimized with oneAPI Deep Neural Network Library (oneDNN) to use the following CPU instructions in performance-critical operations: AVX2 FMA To enable them in other operations, rebuild TensorFlow with the appropriate compiler flags.
Let’s display the architecture of your model so far:
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 (MaxPooling (None, 6, 6, 64) 0 2D) conv2d_2 (Conv2D) (None, 4, 4, 64) 36928 ================================================================= Total params: 56,320 Trainable params: 56,320 Non-trainable params: 0 _________________________________________________________________
Above, you can see that the output of every Conv2D and MaxPooling2D layer is a 3D tensor of shape (height, width, channels). The width and height dimensions tend to shrink as you go deeper in the network. The number of output channels for each Conv2D layer is controlled by the first argument (e.g., 32 or 64). Typically, as the width and height shrink, you can afford (computationally) to add more output channels in each Conv2D layer.
Add Dense layers on top#
To complete the model, you will feed the last output tensor from the convolutional base (of shape (4, 4, 64)) into one or more Dense layers to perform classification. Dense layers take vectors as input (which are 1D), while the current output is a 3D tensor. First, you will flatten (or unroll) the 3D output to 1D, then add one or more Dense layers on top. CIFAR has 10 output classes, so you use a final Dense layer with 10 outputs.
model.add(layers.Flatten()) model.add(layers.Dense(64, activation='relu')) model.add(layers.Dense(10))
Here’s the complete architecture of your model:
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 (MaxPooling (None, 6, 6, 64) 0 2D) 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 _________________________________________________________________
The network summary shows that (4, 4, 64) outputs were flattened into vectors of shape (1024) before going through two Dense layers.
Compile and train the model#
model.compile(optimizer='adam', loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), metrics=['accuracy']) history = model.fit(train_images, train_labels, epochs=5, validation_data=(test_images, test_labels))
Epoch 1/5 1563/1563 [==============================] - 30s 19ms/step - loss: 0.7346 - accuracy: 0.7421 - val_loss: 0.9005 - val_accuracy: 0.7014 Epoch 2/5 1563/1563 [==============================] - 29s 19ms/step - loss: 0.6875 - accuracy: 0.7578 - val_loss: 0.8748 - val_accuracy: 0.7038 Epoch 3/5 1563/1563 [==============================] - 30s 19ms/step - loss: 0.6498 - accuracy: 0.7712 - val_loss: 0.8606 - val_accuracy: 0.7041 Epoch 4/5 1563/1563 [==============================] - 30s 19ms/step - loss: 0.6073 - accuracy: 0.7852 - val_loss: 0.8850 - val_accuracy: 0.6981 Epoch 5/5 1563/1563 [==============================] - 28s 18ms/step - loss: 0.5764 - accuracy: 0.7955 - val_loss: 0.8740 - val_accuracy: 0.7124
Evaluate the model#
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') test_loss, test_acc = model.evaluate(test_images, test_labels, verbose=2)
313/313 - 1s - loss: 0.8475 - accuracy: 0.7192 - 634ms/epoch - 2ms/step
Your simple CNN has achieved a test accuracy of over 70%. Not bad for a few lines of code! For another CNN style, check out the TensorFlow 2 quickstart for experts example that uses the Keras subclassing API and