tensorflow数据加载之DataSet

青旅半醒 2022-02-22 23:56 310阅读 0赞

话不多说，干就完了。

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在上一篇博文中简单介绍了一下TFRecord数据格式的生成和加载，本篇介绍另一种数据加载方式DataSet。

不管何种类型的数据加载方式都遵循一下几个步骤：

1.  遍历原始图像数据集中的所有图片
2.  读取图片和对应的类别标签
3.  将读取到的图片向量输入模型用于训练

下面就讲一下DataSet加载图像数据的使用方法：

前提：本文使用的测试数据集只有6张图片，猫狗各三张，数据集目录结构如下：

![20190405140835164.png][]

1）、读取原始数据信息，并保存到txt文件中，保存格式为：

图像地址         图像标签（从0开始，依次递增，方便后续进行one-hot编码）

import os
    
    current_path = os.path.dirname(os.path.abspath(__file__))
    datasets_path = os.path.join(current_path, "dataset")
    filename = os.path.join(current_path, "dataset_image_list.txt")
    
    if os.path.exists(filename) is False:
        with open(filename, "w") as f_obj:
            for cls_index, cls_name in enumerate(os.listdir(datasets_path)):
                print(cls_name)
                if os.path.isdir(os.path.join(datasets_path, cls_name)):
                    print("#" * 40, cls_name, "#" * 40)
                    for img_index, img_name in enumerate(os.listdir(os.path.join(datasets_path, cls_name))):
                        if os.path.isfile(os.path.join(datasets_path, cls_name, img_name)):
                            img_path = os.path.join(datasets_path, cls_name, img_name)
                            f_obj.write(img_path + "\t" + str(cls_index) + "\n")
    else:
        print("file exists")

将图像数据信息先读取到txt文件中的好处还有一个是，后面对图像进行处理，不管是生成TFRecord还是DataSet的过程中，都方便对数据集进行重排shuffle，不然的话就是连续的读取相同类型标签的图像，在网络训练时还需要再次进行重排shuffle。

2）、加载第一步生成的txt文件，将其中的图像信息保存到TFRecord文件中

import os
    import cv2
    import tensorflow as tf
    from matplotlib import pyplot as plt
    import numpy as np
    
    current_path = os.path.dirname(os.path.abspath(__file__))
    datasets_path = os.path.join(current_path, "dataset_image_list.txt")
    train_tfreocrd_filename = os.path.join(current_path, "tfrecord_files", "cat_and_dog_train.tfrecords")
    validation_tfreocrd_filename = os.path.join(current_path, "tfrecord_files", "cat_and_dog_validation.tfrecords")
    image_size = 224
    image_channel = 3
    
    
    def generate_tfrecord():
        if os.path.exists(train_tfreocrd_filename):
            return
    
        def _int64_feature(value):
            return tf.train.Feature(int64_list=tf.train.Int64List(value=[value]))
    
        def _bytes_feature(value):
            return tf.train.Feature(bytes_list=tf.train.BytesList(value=[value]))
    
        train_writer = tf.python_io.TFRecordWriter(path=train_tfreocrd_filename)
        validation_writer = tf.python_io.TFRecordWriter(path=validation_tfreocrd_filename)
    
        with open(datasets_path, "r") as f_obj:
            image_list = f_obj.readlines()
            image_list_len = len(image_list)
            print(image_list_len)
            permutation = np.random.permutation(image_list_len)
            print(permutation)
    
            img_list = []
            for i in permutation:
                img_list.append(image_list[i])
    
            for img_index, img_info in enumerate(img_list):
                img_path, img_class = img_info.split()
                img_class = int(img_class)
                print(img_path, img_class)
    
                if os.path.isfile(img_path):
                    img = cv2.imread(filename=img_path)
    
                    if img.ndim == image_channel:
                        img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
                        img = cv2.resize(img, (image_size, image_size), cv2.INTER_AREA)
                        img_pixles = img.shape[0] * img.shape[1] * img.shape[2]
    
                        # plt.imshow(img)
                        # plt.show()
                    else:
                        continue
                    image_raw = img.tostring()
                    # print(image_raw)
    
                    example = tf.train.Example(
                        features=tf.train.Features(
                            feature={
                                "pixels": _int64_feature(img_pixles),
                                "label": _int64_feature(img_class),
                                "image_raw": _bytes_feature(image_raw)
                            }
                        )
                    )
    
                    if img_index % 2 == 0:
                        validation_writer.write(example.SerializeToString())
                    else:
                        train_writer.write(example.SerializeToString())
        train_writer.close()
        validation_writer.close()
    
    
    def read_from_tfrecord(sess):
        reader = tf.TFRecordReader()
    
        filename_queue = tf.train.string_input_producer(
            string_tensor=[train_tfreocrd_filename, validation_tfreocrd_filename])
    
        _, serialized_example = reader.read(filename_queue)
    
        features = tf.parse_single_example(
            serialized_example,
            features={
                "pixels": tf.FixedLenFeature([], tf.int64),
                "label": tf.FixedLenFeature([], tf.int64),
                "image_raw": tf.FixedLenFeature([], tf.string)
            }
        )
    
        image = tf.decode_raw(features['image_raw'], tf.uint8)
        label = tf.cast(features["label"], tf.int64)
        pixels = tf.cast(features["pixels"], tf.int32)
    
        coord = tf.train.Coordinator()
        threads = tf.train.start_queue_runners(sess=sess, coord=coord)
    
        for i in range(6):
            image_raw, image_label, _ = sess.run([image, label, pixels])
            image_raw = np.reshape(image_raw, (image_size, image_size, image_channel))
            print(image_raw.shape)
            plt.imshow(image_raw)
            plt.xlabel(str(image_label))
            plt.show()
    
    
    if __name__ == '__main__':
        with tf.Session() as sess:
            generate_tfrecord()
            read_from_tfrecord(sess=sess)

3）、基于第二步生成的TFRecord文件构造DataSet

import os
    import tensorflow as tf
    import cv2
    
    
    def _parse_tfrecord_features(serialized_feature):
        features = {
            "pixels": tf.FixedLenFeature([], tf.int64),
            "label": tf.FixedLenFeature([], tf.int64),
            "image_raw": tf.FixedLenFeature([], tf.string)
        }
        image_features = tf.parse_single_example(
            serialized_feature,
            features=features
        )
        image_raw = tf.decode_raw(bytes=image_features["image_raw"], out_type=tf.uint8)
        image_raw = tf.image.convert_image_dtype(image_raw, tf.float32)
    
        labels = tf.cast(image_features["label"], tf.int64)
        image_labels = tf.one_hot(labels, depth=2)
    
        return image_raw, image_labels
    
    def _image_reshape(image_data, image_label):
        return tf.reshape(image_data, (224, 224, 3)), image_label
    
    current_path = os.path.dirname(os.path.abspath(__file__))
    train_tfrecords = os.path.join(current_path, "tfrecord_files", "cat_and_dog_train.tfrecords")
    validation_tfrecords = os.path.join(current_path, "tfrecord_files", "cat_and_dog_validation.tfrecords")
    repeat_count = 3
    batch_size = 16
    shuffle_buffer_size = 4096
    train_epoch = 10
    image_size = 224
    image_channel = 3
    
    train_tfrecord_datasets = tf.data.TFRecordDataset(filenames=train_tfrecords)
    train_tfrecord_datasets = train_tfrecord_datasets.map(_parse_tfrecord_features)
    train_tfrecord_datasets = train_tfrecord_datasets.repeat(count=repeat_count)
    train_tfrecord_datasets = train_tfrecord_datasets.map(_image_reshape)
    
    train_tfrecord_datasets = train_tfrecord_datasets.shuffle(buffer_size=shuffle_buffer_size,
                                                              reshuffle_each_iteration=True)
    train_tfrecord_datasets_batch = train_tfrecord_datasets.batch(batch_size=batch_size)
    
    validation_tfrecord_datasets = tf.data.TFRecordDataset(filenames=validation_tfrecords)
    validation_tfrecord_datasets = validation_tfrecord_datasets.map(_parse_tfrecord_features)
    validation_tfrecord_datasets = validation_tfrecord_datasets.map(_image_reshape)
    validation_tfrecord_datasets = validation_tfrecord_datasets.shuffle(buffer_size=shuffle_buffer_size, reshuffle_each_iteration=True)
    validation_tfrecord_datasets_batch = validation_tfrecord_datasets.batch(batch_size=batch_size)
    
    iterator = tf.data.Iterator.from_structure(
        output_types=train_tfrecord_datasets_batch.output_types,
        output_shapes=train_tfrecord_datasets_batch.output_shapes
    )
    
    train_init_op = iterator.make_initializer(dataset=train_tfrecord_datasets_batch)
    validation_init_op = iterator.make_initializer(dataset=validation_tfrecord_datasets_batch)
    
    next_batch = iterator.get_next()
    
    if __name__ == '__main__':
        with tf.Session() as sess:
            for epoch in range(train_epoch):
                sess.run(train_init_op)
                print("#" * 30, "training", "#" * 30)
                while True:
                    try:
                        train_data_batch, train_label_batch = sess.run(next_batch)
                        print(train_label_batch)
                    except tf.errors.OutOfRangeError as e:
                        # print(e)
                        break
    
                print("#" * 30, "validation", "#" * 30)
                sess.run(validation_init_op)
                while True:
                    try:
                        validation_data_batch, validation_label_batch = sess.run(next_batch)
                        print(validation_label_batch)
                    except tf.errors.OutOfRangeError as e:
                        # print(e)
                        break

其中几个要点需要说明一下：

1）、\_parse\_tfrecord\_features函数用于解析TFRecord文件中图像信息，也就是需要将TFRecord中保存的图像矩阵和图像标签one-hot编码解析出来

2）、\_image\_reshape函数是将解析后的图像矩阵还原为3维（224，224，3）的形状

3）、train\_tfrecord\_datasets.map(\_parse\_tfrecord\_features)和train\_tfrecord\_datasets.map(\_image\_reshape)

函数是分别对dataset中的每个元素应用一次\_parse\_tfrecord\_features和\_image\_reshape，从而符合神经网络输入的DataSet

4）、由于训练数据和验证数据具有相同的结构，所以tf.data.Iterator.from\_structure来构造迭代器对象，注意用的是train\_tfrecord\_datasets\_batch

iterator = tf.data.Iterator.from_structure(
        output_types=train_tfrecord_datasets_batch.output_types,
        output_shapes=train_tfrecord_datasets_batch.output_shapes
    )

5）、以下两步是对训练数据Dataset和验证数据DataSet进行初始化

train\_init\_op = iterator.make\_initializer(dataset=train\_tfrecord\_datasets\_batch)  
validation\_init\_op = iterator.make\_initializer(dataset=validation\_tfrecord\_datasets\_batch)

6）、当需要使用训练数据时，先执行sess.run(train\_init\_op)进行初始化，然后再执行train\_data\_batch, train\_label\_batch = sess.run(next\_batch)即可获得训练用的batch；同理，需要使用验证数据时，先执行sess.run(validation\_init\_op)，然后再执行validation\_data\_batch, validation\_label\_batch = sess.run(next\_batch)即可获得验证用的batch.

注意：随着iterator不断的取next，当取到最后的时候会抛出tf.errors.OutOfRangeError异常，表示数据已经取完了，此时如果想要进行下一轮的取数据则需要执行相应的初始化操作（train\_init\_op或validation\_init\_op）\_batch)即可获得验证用的batch.

注意：随着iterator不断的取next，当取到最后的时候会抛出tf.errors.OutOfRangeError异常，表示数据已经取完了，此时如果想要进行下一轮的取数据则需要执行相应的初始化操作（train\_init\_op或validation\_init\_op）

[20190405140835164.png]: /images/20220223/fdf2dbb353484dcdbf9fba2e03437f9a.png