feature -> Features -> Example, 三者按顺序为包含关系

example = tf.train.Example(features=tf.train.Features(feature={...}))
tf_writer.write(example.SerializeToString())  # 序列化写入tfrecord

注意: feature必须是list, 可以先转成ndarray再转回来

def _convert_to_example(image_name, labels, labels_text, bboxes, oriented_bboxes, shape,
                        difficult=0, truncated=0):
    """Build an Example proto for an image example.

    Args:
      image_data: string, JPEG encoding of RGB image;
      labels: list of integers, identifier for the ground truth;
      labels_text: list of text-string;
      bboxes: list of bounding boxes; each box is a list of integers;
          specifying [xmin, ymin, xmax, ymax]. All boxes are assumed to belong
          to the same label as the image label.
      shape: 3 integers, image shapes in pixels.
    Returns:
      Example proto
    """
    image_data = tf.gfile.FastGFile(image_name, 'rb').read()
    image_format = b'JPG'
    # Example protocol对象就是对图片加上bbox等位置信息的一种封装
    example = tf.train.Example(features=tf.train.Features(feature={
        'image/shape': int64_feature(shape),
        'image/object/bbox/xmin': float_feature(bboxes[0]),
        'image/object/bbox/ymin': float_feature(bboxes[1]),
        'image/object/bbox/xmax': float_feature(bboxes[2]),
        'image/object/bbox/ymax': float_feature(bboxes[3]),
        'image/object/bbox/x1': float_feature(list(oriented_bboxes[:, 0])),
        'image/object/bbox/x2': float_feature(list(oriented_bboxes[:, 1])),
        'image/object/bbox/x3': float_feature(list(oriented_bboxes[:, 2])),
        'image/object/bbox/x4': float_feature(list(oriented_bboxes[:, 3])),
        'image/object/bbox/y1': float_feature(list(oriented_bboxes[:, 4])),
        'image/object/bbox/y2': float_feature(list(oriented_bboxes[:, 5])),
        'image/object/bbox/y3': float_feature(list(oriented_bboxes[:, 6])),
        'image/object/bbox/y4': float_feature(list(oriented_bboxes[:, 7])),
        'image/object/bbox/label': int64_feature(labels),
        'image/object/bbox/label_text': bytes_feature(labels_text),
        'image/object/bbox/difficult': int64_feature(difficult),
        'image/object/bbox/truncated': int64_feature(truncated),
        'image/format': bytes_feature(image_format),
        'image/filename': bytes_feature(image_name.encode()),
        'image/encoded': bytes_feature(image_data)
        })
    )
    return example

参考https://blog.csdn.net/hfutdog/article/details/86244944

python3下string和byte编码问题

对Example中的features进行feature输入时, python3会报错,'*.jpg' has type str, but expected one of: bytes, 是因为python3中string和byte不能互相转换, 必须通过str.encode() -> byte或者byte.decode() -> string, 如:

'image/format': bytes_feature(image_format),
'image/filename': bytes_feature(image_name.encode()),
'image/encoded': bytes_feature(image_data)

或在一开始读文件和输入字符串的时候就指定成二进制, 通过加b实现:

image_data = tf.gfile.FastGFile(image_name, 'rb').read()
image_format = b'JPG'