TensorFlow学习系列09 | 优化猫狗识别

技术小黑2026-04-03 10:53

一、前置知识

1、VGG-16算法介绍

VGG-16 是深度学习计算机视觉领域中非常著名且经典的卷积神经网络（CNN）模型，由牛津大学的 Visual Geometry Group (VGG) 提出。它在 2014 年的 ImageNet 竞赛中取得了极好的成绩，并且因为其结构简洁、规整，至今仍常被用作教学示例或特征提取的基础模型。

VGG-16 最显著的特点就是它的"深度"（16层带权重的层）以及它对小尺寸卷积核（3x3）的坚持使用。我们可以一起来探索它的奥秘。

1.1、网络架构与"积木"结构

为了理解 VGG-16 的架构，我们可以把它想象成一个"5级浓缩果汁加工厂"。

1.2、核心创新：为什么是 3x3？

为了理解为什么要"舍大求小"，我们可以想象 "警察审讯嫌疑人" 的场景。

1.3、从输入到输出的流程

把 VGG-16 想象成一条"数据流水线"。我们将追踪一张猫的照片**（224 * 224 像素）是如何进入网络，被层层"扒皮"，最后变成一个简单的单词"Cat"的。

到现在为止，你已经掌握了 VGG-16 的架构 (2-2-3-3-3) 、核心原理 (小卷积核) 以及数据流向 (宽变窄，薄变厚)。

二、代码实现

1、准备工作

1.1.设置GPU

复制代码 
import tensorflow as tf
gpus = tf.config.list_physical_devices("GPU")

if gpus:
    gpu0 = gpus[0] #如果有多个GPU，仅使用第0个GPU
    tf.config.experimental.set_memory_growth(gpu0, True) #设置GPU显存用量按需使用
    tf.config.set_visible_devices([gpu0],"GPU")
    
print(gpus)

2026-04-02 08:55:14.743628: I tensorflow/core/util/util.cc:169] oneDNN custom operations are on. You may see slightly different numerical results due to floating-point round-off errors from different computation orders. To turn them off, set the environment variable `TF_ENABLE_ONEDNN_OPTS=0`.
[PhysicalDevice(name='/physical_device:GPU:0', device_type='GPU')]

1.2.导入数据

复制代码 
import os,PIL,pathlib
import matplotlib.pyplot as plt
import numpy             as np
from tensorflow          import keras
from tensorflow.keras    import layers,models

# 查看当前工作路径（确认路径是否正确）
print("当前工作路径：", os.getcwd())

# 定义数据目录（建议用绝对路径更稳妥，相对路径依赖当前工作路径）
data_dir = './data/day09/'
data_dir = pathlib.Path(data_dir)

# 获取数据目录下的所有子路径（文件夹或文件）
data_paths = list(data_dir.glob('*'))

# 提取每个子路径的名称（即类别名，自动适配系统分隔符）
classeNames = [path.name for path in data_paths]
classeNames

当前工作路径： /root/autodl-tmp/TensorFlow2

['cat', 'dog']

1.3.查看数据

复制代码 
image_count = len(list(data_dir.glob('*/*')))
print("图片总数为：",image_count)

图片总数为： 3400

1.4.可视化图片

复制代码 
roses = list(data_dir.glob('dog/*.jpg'))
PIL.Image.open(str(roses[0]))

2、数据预处理

2.1.加载数据

  • 使用image_dataset_from_directory方法将磁盘中的数据加载到tf.data.Dataset中

    batch_size = 64
    img_height = 224
    img_width = 224

    #训练集
    train_ds = tf.keras.preprocessing.image_dataset_from_directory(
    data_dir,
    validation_split=0.2,
    subset="training",
    seed=12,
    image_size=(img_height, img_width),
    batch_size=batch_size)

    Found 3400 files belonging to 2 classes.
    Using 2720 files for training.

    2026-04-02 09:10:01.194533: I tensorflow/core/platform/cpu_feature_guard.cc:193] This TensorFlow binary is optimized with oneAPI Deep Neural Network Library (oneDNN) to use the following CPU instructions in performance-critical operations: AVX2 AVX512F AVX512_VNNI FMA
    To enable them in other operations, rebuild TensorFlow with the appropriate compiler flags.
    2026-04-02 09:10:02.440253: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1532] Created device /job:localhost/replica:0/task:0/device:GPU:0 with 9960 MB memory: -> device: 0, name: NVIDIA GeForce RTX 3080 Ti, pci bus id: 0000:d9:00.0, compute capability: 8.6

    验证集

    val_ds = tf.keras.preprocessing.image_dataset_from_directory(
    data_dir,
    validation_split=0.2,
    subset="validation",
    seed=12,
    image_size=(img_height, img_width),
    batch_size=batch_size)

    Found 3400 files belonging to 2 classes.
    Using 680 files for validation.

    class_names = train_ds.class_names
    print(class_names)

    ['cat', 'dog']

2.2.检查数据

  • Image_batch是形状的张量（32,180,180,3）。这是一批形状180x180x3的32张图片（最后一维指的是彩色通道RGB）。

  • Label_batch是形状（32，）的张量，这些标签对应32张图片

    for image_batch, labels_batch in train_ds:
    print(image_batch.shape)
    print(labels_batch.shape)
    break

    (64, 224, 224, 3)
    (64,)

2.3.配置数据集

  • shuffle() ：打乱数据，关于此函数的详细介绍可以参考
  • prefetch() ：预取数据，加速运行

  • cache() ：将数据集缓存到内存当中，加速运行

    AUTOTUNE = tf.data.AUTOTUNE

    def preprocess_image(image,label):
    return (image/255.0,label)

    归一化处理

    train_ds = train_ds.map(preprocess_image, num_parallel_calls=AUTOTUNE)
    val_ds = val_ds.map(preprocess_image, num_parallel_calls=AUTOTUNE)

    train_ds = train_ds.cache().shuffle(1000).prefetch(buffer_size=AUTOTUNE)
    val_ds = val_ds.cache().prefetch(buffer_size=AUTOTUNE)

2.4. 可视化数据

复制代码 
plt.figure(figsize=(15, 10))  # 图形的宽为15高为10

for images, labels in train_ds.take(1):
    for i in range(8):
        
        ax = plt.subplot(5, 8, i + 1) 
        plt.imshow(images[i])
        plt.title(class_names[labels[i]])
        
        plt.axis("off")

3、训练模型

3.1.构建VGG-16网络

  • VGG优点:
    VGG的结构非常简洁，整个网络都使用了同样大小的卷积核尺寸（3x3）和最大池化尺寸（2x2）。
  • VGG缺点:
    1. 训练时间过长，调参难度大。
    1. 需要的存储容量大，不利于部署。例如存储VGG-16权重值文件的大小为500多MB，不利于安装到嵌入式系统中。
  • 结构说明:
    1. 13个卷积层（Convolutional Layer），分别用blockX_convX表示
    1. 3个全连接层（Fully connected Layer），分别用fcX与predictions表示
    1. 5个池化层（Pool layer），分别用blockX_pool表示

  • VGG-16包含了16个隐藏层（13个卷积层和3个全连接层），故称为VGG-16

    from tensorflow.keras import layers, models, Input
    from tensorflow.keras.models import Model
    from tensorflow.keras.layers import Conv2D, MaxPooling2D, Dense, Flatten, Dropout

    def VGG16(nb_classes, input_shape):
    input_tensor = Input(shape=input_shape)
    # 1st block
    x = Conv2D(64, (3,3), activation='relu', padding='same',name='block1_conv1')(input_tensor)
    x = Conv2D(64, (3,3), activation='relu', padding='same',name='block1_conv2')(x)
    x = MaxPooling2D((2,2), strides=(2,2), name = 'block1_pool')(x)
    # 2nd block
    x = Conv2D(128, (3,3), activation='relu', padding='same',name='block2_conv1')(x)
    x = Conv2D(128, (3,3), activation='relu', padding='same',name='block2_conv2')(x)
    x = MaxPooling2D((2,2), strides=(2,2), name = 'block2_pool')(x)
    # 3rd block
    x = Conv2D(256, (3,3), activation='relu', padding='same',name='block3_conv1')(x)
    x = Conv2D(256, (3,3), activation='relu', padding='same',name='block3_conv2')(x)
    x = Conv2D(256, (3,3), activation='relu', padding='same',name='block3_conv3')(x)
    x = MaxPooling2D((2,2), strides=(2,2), name = 'block3_pool')(x)
    # 4th block
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block4_conv1')(x)
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block4_conv2')(x)
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block4_conv3')(x)
    x = MaxPooling2D((2,2), strides=(2,2), name = 'block4_pool')(x)
    # 5th block
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block5_conv1')(x)
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block5_conv2')(x)
    x = Conv2D(512, (3,3), activation='relu', padding='same',name='block5_conv3')(x)
    x = MaxPooling2D((2,2), strides=(2,2), name = 'block5_pool')(x)
    # full connection
    x = Flatten()(x)
    x = Dense(4096, activation='relu', name='fc1')(x)
    x = Dense(4096, activation='relu', name='fc2')(x)
    output_tensor = Dense(nb_classes, activation='softmax', name='predictions')(x)

    复制代码 
      model = Model(input_tensor, output_tensor)
  return model

    model=VGG16(1000, (img_width, img_height, 3))
    model.summary()

    Model: "model"

    Layer (type) Output Shape Param #

    input_1 (InputLayer) [(None, 224, 224, 3)] 0

    block1_conv1 (Conv2D) (None, 224, 224, 64) 1792

    block1_conv2 (Conv2D) (None, 224, 224, 64) 36928

    block1_pool (MaxPooling2D) (None, 112, 112, 64) 0

    block2_conv1 (Conv2D) (None, 112, 112, 128) 73856

    block2_conv2 (Conv2D) (None, 112, 112, 128) 147584

    block2_pool (MaxPooling2D) (None, 56, 56, 128) 0

    block3_conv1 (Conv2D) (None, 56, 56, 256) 295168

    block3_conv2 (Conv2D) (None, 56, 56, 256) 590080

    block3_conv3 (Conv2D) (None, 56, 56, 256) 590080

    block3_pool (MaxPooling2D) (None, 28, 28, 256) 0

    block4_conv1 (Conv2D) (None, 28, 28, 512) 1180160

    block4_conv2 (Conv2D) (None, 28, 28, 512) 2359808

    block4_conv3 (Conv2D) (None, 28, 28, 512) 2359808

    block4_pool (MaxPooling2D) (None, 14, 14, 512) 0

    block5_conv1 (Conv2D) (None, 14, 14, 512) 2359808

    block5_conv2 (Conv2D) (None, 14, 14, 512) 2359808

    block5_conv3 (Conv2D) (None, 14, 14, 512) 2359808

    block5_pool (MaxPooling2D) (None, 7, 7, 512) 0

    flatten (Flatten) (None, 25088) 0

    fc1 (Dense) (None, 4096) 102764544

    fc2 (Dense) (None, 4096) 16781312

    predictions (Dense) (None, 1000) 4097000

    =================================================================
    Total params: 138,357,544
    Trainable params: 138,357,544
    Non-trainable params: 0

3.2.编译模型

在准备对模型进行训练之前，还需要再对其进行一些设置。以下内容是在模型的编译步骤中添加的：

  • 损失函数（loss）：用于衡量模型在训练期间的准确率。
  • 优化器（optimizer）：决定模型如何根据其看到的数据和自身的损失函数进行更新。

  • 评价函数（metrics）：用于监控训练和测试步骤。以下示例使用了准确率，即被正确分类的图像的比率。

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

3.3.训练模型

复制代码 
from tqdm import tqdm
import tensorflow.keras.backend as K

epochs = 10
lr     = 1e-4

# 记录训练数据，方便后面的分析
history_train_loss     = []
history_train_accuracy = []
history_val_loss       = []
history_val_accuracy   = []

for epoch in range(epochs):
    train_total = len(train_ds)
    val_total   = len(val_ds)
    
    """
    total：预期的迭代数目
    ncols：控制进度条宽度
    mininterval：进度更新最小间隔，以秒为单位（默认值：0.1）
    """
    with tqdm(total=train_total, desc=f'Epoch {epoch + 1}/{epochs}',mininterval=1,ncols=100) as pbar:
        
        lr = lr*0.92
        K.set_value(model.optimizer.lr, lr)
        
        train_loss     = []
        train_accuracy = []
        for image,label in train_ds:   
            """
            训练模型，简单理解train_on_batch就是：它是比model.fit()更高级的一个用法
            """
             # 这里生成的是每一个batch的acc与loss
            history = model.train_on_batch(image,label)
            
            train_loss.append(history[0])
            train_accuracy.append(history[1])
            
            pbar.set_postfix({"train_loss": "%.4f"%history[0],
                              "train_acc":"%.4f"%history[1],
                              "lr": K.get_value(model.optimizer.lr)})
            pbar.update(1)
            
        history_train_loss.append(np.mean(train_loss))
        history_train_accuracy.append(np.mean(train_accuracy))
            
    print('开始验证！')
    
    with tqdm(total=val_total, desc=f'Epoch {epoch + 1}/{epochs}',mininterval=0.3,ncols=100) as pbar:

        val_loss     = []
        val_accuracy = []
        for image,label in val_ds:      
            # 这里生成的是每一个batch的acc与loss
            history = model.test_on_batch(image,label)
            
            val_loss.append(history[0])
            val_accuracy.append(history[1])
            
            pbar.set_postfix({"val_loss": "%.4f"%history[0],
                              "val_acc":"%.4f"%history[1]})
            pbar.update(1)
        history_val_loss.append(np.mean(val_loss))
        history_val_accuracy.append(np.mean(val_accuracy))
            
    print('结束验证！')
    print("验证loss为：%.4f"%np.mean(val_loss))
    print("验证准确率为：%.4f"%np.mean(val_accuracy))

Epoch 1/10:   0%|                                                            | 0/43 [00:00<?, ?it/s]2026-04-02 09:18:40.335169: I tensorflow/stream_executor/cuda/cuda_dnn.cc:384] Loaded cuDNN version 8101
2026-04-02 09:18:47.267058: W tensorflow/core/common_runtime/bfc_allocator.cc:360] Garbage collection: deallocate free memory regions (i.e., allocations) so that we can re-allocate a larger region to avoid OOM due to memory fragmentation. If you see this message frequently, you are running near the threshold of the available device memory and re-allocation may incur great performance overhead. You may try smaller batch sizes to observe the performance impact. Set TF_ENABLE_GPU_GARBAGE_COLLECTION=false if you'd like to disable this feature.
Epoch 1/10: 100%|███| 43/43 [00:22<00:00,  1.90it/s, train_loss=0.7120, train_acc=0.5156, lr=9.2e-5]
开始验证！
Epoch 1/10: 100%|██████████████████| 11/11 [00:02<00:00,  4.19it/s, val_loss=0.7243, val_acc=0.5250]
结束验证！
验证loss为：0.6862
验证准确率为：0.5193
....

Epoch 10/10: 100%|█| 43/43 [00:11<00:00,  3.82it/s, train_loss=0.0604, train_acc=0.9844, lr=4.34e-5]
开始验证！
Epoch 10/10: 100%|█████████████████| 11/11 [00:01<00:00,  9.02it/s, val_loss=0.0716, val_acc=0.9750]
结束验证！
验证loss为：0.0554
验证准确率为：0.9793

4、模型评估

4.1.Loss与Accuracy图

复制代码 
from datetime import datetime
current_time = datetime.now() # 获取当前时间

epochs_range = range(epochs)

plt.figure(figsize=(14, 4))
plt.subplot(1, 2, 1)

plt.plot(epochs_range, history_train_accuracy, label='Training Accuracy')
plt.plot(epochs_range, history_val_accuracy, label='Validation Accuracy')
plt.legend(loc='lower right')
plt.title('Training and Validation Accuracy')
plt.xlabel(current_time) # 打卡请带上时间戳，否则代码截图无效

plt.subplot(1, 2, 2)
plt.plot(epochs_range, history_train_loss, label='Training Loss')
plt.plot(epochs_range, history_val_loss, label='Validation Loss')
plt.legend(loc='upper right')
plt.title('Training and Validation Loss')
plt.show()

5、图片预测

复制代码 
import numpy as np

# 采用加载的模型（new_model）来看预测结果
plt.figure(figsize=(18, 3))  # 图形的宽为18高为5
plt.suptitle("predict result")

for images, labels in val_ds.take(1):
    for i in range(8):
        ax = plt.subplot(1,8, i + 1)  
        
        # 显示图片
        plt.imshow(images[i].numpy())
        
        # 需要给图片增加一个维度
        img_array = tf.expand_dims(images[i], 0) 
        
        # 使用模型预测图片中的人物
        predictions = model.predict(img_array)
        plt.title(class_names[np.argmax(predictions)])

        plt.axis("off")

1/1 [==============================] - 0s 29ms/step
1/1 [==============================] - 0s 27ms/step
1/1 [==============================] - 0s 23ms/step
1/1 [==============================] - 0s 26ms/step
1/1 [==============================] - 0s 27ms/step
1/1 [==============================] - 0s 25ms/step
1/1 [==============================] - 0s 25ms/step
1/1 [==============================] - 0s 24ms/step
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