使用生成器从成批的 .npy 文件训练 Keras 模型?

问题描述

目前我正在处理使用 Keras 训练图像数据时的大数据问题.我有包含一批 .npy 文件的目录.每批包含 512 张图像.每个批次都有其对应的标签文件为 .npy.所以它看起来像:{image_file_1.npy, label_file_1.npy, ..., image_file_37.npy, label_file_37}.每个图像文件都有维度 (512, 199, 199, 3)，每个标签文件都有维度 (512, 1)(eather 1 or 0) .如果我在一个 ndarray 中加载所有图像，它将是 35+ GB.到目前为止阅读了所有 Keras Doc.我仍然无法找到如何使用自定义生成器进行训练.我已经阅读了 flow_from_dict 和 ImageDataGenerator(...).flow() 但在这种情况下它们并不理想，或者我不知道如何自定义它们.这里是什么我已经做好了.

Currently I am dealing with a big data issue when training Image data using Keras. I have directory which has batch of .npy file. Each batch contain 512 images. Each batch has its corresponding label file as .npy. So it looks like: {image_file_1.npy, label_file_1.npy, ..., image_file_37.npy, label_file_37}. Each image file has dimension (512, 199, 199, 3), each label file has dimension (512, 1)(eather 1 or 0) . If I load all the images in one ndarray it will be 35+ GB. So far reading all the Keras Doc. I am still not able to find how I will be able to train using custom generator. I have read about flow_from_dict and ImageDataGenerator(...).flow() but they are not ideal in that case or I do not know how to customized them.Here what I have done.

import numpy as np
import keras
from keras.models import Sequential
from keras.layers import Dense, Dropout, Flatten
from keras.layers import Conv2D, MaxPooling2D
from keras.optimizers import SGD
from keras.preprocessing.image import ImageDataGenerator

val_gen = ImageDataGenerator(rescale=1./255)
x_test = np.load("../data/val_file.npy")
y_test = np.load("../data/val_label.npy")
val_gen.fit(x_test)

model = Sequential()
...
model_1.add(layers.Dense(512, activation='relu'))
model_1.add(layers.Dense(1, activation='sigmoid'))

model.compile(loss='categorical_crossentropy', 
              optimizer=sgd, 
               metrics=['acc'])

model.fit_generator(generate_batch_from_directory() # should give 1 image file and 1 label file
                    validation_data=val_gen.flow(x_test, 
                                                 y_test, 
                                                 batch_size=64),
                    validation_steps=32)

所以这里 generate_batch_from_directory() 应该每次都取 image_file_i.npy 和 label_file_i.npy 并优化权重直到没有batch..npy 文件中的每个图像数组都已经过增强、旋转和缩放处理.每个 .npy 文件都与类 1 和类 0 (50/50) 的数据正确混合.

So here generate_batch_from_directory() should take image_file_i.npy and label_file_i.npy every time and optimise the weight until there is no batch left. Each image array in the .npy files has already been processed with augmentation, rotation and scaling. Each .npy file is properly mixed with data from class 1 and 0 (50/50).

如果我附加所有批次并创建一个大文件，例如:

If I append all the batch and create a big file such as:

X_train = np.append([image_file_1, ..., image_file_37])
y_train = np.append([label_file_1, ..., label_file_37])

它不适合内存.否则我可以使用 .flow() 生成图像集来训练模型.

It does not fit in the memory. Otherwise I could use .flow() to generate image sets to train the model.

感谢您的建议.

推荐答案

最后我能够解决这个问题.但是我必须通过 keras.utils.Sequence 的源代码和文档来构建我自己的生成器类.本文档对了解发电机在 Kears 中的工作原理.您可以在我的 kaggle notebook:

Finally I was able to solve that problem. But I had to go through source code and documentation of keras.utils.Sequence to build my own generator class. This document help a lot to understand how generator works in Kears. You can read more detail in my kaggle notebook:

all_files_loc = "datapsycho/imglake/population/train/image_files/"
all_files = os.listdir(all_files_loc)

image_label_map = {
        "image_file_{}.npy".format(i+1): "label_file_{}.npy".format(i+1)
        for i in range(int(len(all_files)/2))}
partition = [item for item in all_files if "image_file" in item]

class DataGenerator(keras.utils.Sequence):

    def __init__(self, file_list):
        """Constructor can be expanded,
           with batch size, dimentation etc.
        """
        self.file_list = file_list
        self.on_epoch_end()

    def __len__(self):
      'Take all batches in each iteration'
      return int(len(self.file_list))

    def __getitem__(self, index):
      'Get next batch'
      # Generate indexes of the batch
      indexes = self.indexes[index:(index+1)]

      # single file
      file_list_temp = [self.file_list[k] for k in indexes]

      # Set of X_train and y_train
      X, y = self.__data_generation(file_list_temp)

      return X, y

    def on_epoch_end(self):
      'Updates indexes after each epoch'
      self.indexes = np.arange(len(self.file_list))

    def __data_generation(self, file_list_temp):
      'Generates data containing batch_size samples'
      data_loc = "datapsycho/imglake/population/train/image_files/"
      # Generate data
      for ID in file_list_temp:
          x_file_path = os.path.join(data_loc, ID)
          y_file_path = os.path.join(data_loc, image_label_map.get(ID))

          # Store sample
          X = np.load(x_file_path)

          # Store class
          y = np.load(y_file_path)

      return X, y

# ====================
# train set
# ====================
all_files_loc = "datapsycho/imglake/population/train/image_files/"
all_files = os.listdir(all_files_loc)

training_generator = DataGenerator(partition)
validation_generator = ValDataGenerator(val_partition) # work same as training generator

hst = model.fit_generator(generator=training_generator, 
                           epochs=200, 
                           validation_data=validation_generator,
                           use_multiprocessing=True,
                           max_queue_size=32)

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