如何从tensorflow对象检测api的pts标签文件中导出TFRecords？

import tensorflow as tf
import numpy as np
from PIL import Image

def create_tf_example(image_path, labels):
    with tf.gfile.GFile(image_path, 'rb') as fid:
        encoded_image = fid.read()
    
    image = Image.open(image_path)
    width, height = image.size
    
    xmins = []
    xmaxs = []
    ymins = []
    ymaxs = []
    classes_text = []
    classes = []
    
    for label in labels:
        xmins.append(label['xmin'] / width)
        xmaxs.append(label['xmax'] / width)
        ymins.append(label['ymin'] / height)
        ymaxs.append(label['ymax'] / height)
        classes_text.append(label['class'].encode('utf8'))
        classes.append(label['class_id'])
    
    tf_example = tf.train.Example(features=tf.train.Features(feature={
        'image/encoded': tf.train.Feature(bytes_list=tf.train.BytesList(value=[encoded_image])),
        'image/format': tf.train.Feature(bytes_list=tf.train.BytesList(value=['jpeg'.encode('utf8')])),
        'image/object/bbox/xmin': tf.train.Feature(float_list=tf.train.FloatList(value=xmins)),
        'image/object/bbox/xmax': tf.train.Feature(float_list=tf.train.FloatList(value=xmaxs)),
        'image/object/bbox/ymin': tf.train.Feature(float_list=tf.train.FloatList(value=ymins)),
        'image/object/bbox/ymax': tf.train.Feature(float_list=tf.train.FloatList(value=ymaxs)),
        'image/object/class/text': tf.train.Feature(bytes_list=tf.train.BytesList(value=classes_text)),
        'image/object/class/label': tf.train.Feature(int64_list=tf.train.Int64List(value=classes)),
    }))
    
    return tf_example

def main():
    output_path = 'output.tfrecord'
    image_dir = 'images/'
    label_file = 'labels.xml'
    
    writer = tf.python_io.TFRecordWriter(output_path)
    
    # 解析PTS标签文件，获取标签信息
    labels = parse_pascal_voc_xml(label_file)
    
    for label in labels:
        image_path = image_dir + label['filename']
        tf_example = create_tf_example(image_path, label['objects'])
        writer.write(tf_example.SerializeToString())
    
    writer.close()
    print('TFRecords导出完成！')

if __name__ == '__main__':
    main()