将MNIST数据从numpy数组转换为原始ubyte数据

import numpy as np
import struct

# 假设已经加载了MNIST数据集的numpy数组，分别为train_images和train_labels
# train_images的shape为(60000, 28, 28)，train_labels的shape为(60000,)

def convert_to_ubyte(images, labels, output_images_file, output_labels_file):
    num_images = images.shape[0]
    rows = images.shape[1]
    cols = images.shape[2]

    # 将图片数据转换为ubyte格式
    with open(output_images_file, 'wb') as f:
        f.write(struct.pack('>IIII', 2051, num_images, rows, cols))
        for i in range(num_images):
            f.write(struct.pack('B' * rows * cols, *images[i].flatten()))

    # 将标签数据转换为ubyte格式
    with open(output_labels_file, 'wb') as f:
        f.write(struct.pack('>II', 2049, num_images))
        f.write(struct.pack('B' * num_images, *labels))

# 假设输出的ubyte文件名分别为output_images.ubyte和output_labels.ubyte
convert_to_ubyte(train_images, train_labels, 'output_images.ubyte', 'output_labels.ubyte')