readers.py 文件源码

def prepare_serialized_examples(self, serialized_examples, width=50, height=50):
    # set the mapping from the fields to data types in the proto
    feature_map = {
           'image': tf.FixedLenFeature((), tf.string, default_value=''),
           'image_id': tf.FixedLenFeature((), tf.string, default_value=''),
    }
    features = tf.parse_example(serialized_examples, features=feature_map)

    def decode_and_resize(image_str_tensor):
      """Decodes png string, resizes it and returns a uint8 tensor."""

      # Output a grayscale (channels=1) image
      image = tf.image.decode_png(image_str_tensor, channels=1)

      # Note resize expects a batch_size, but tf_map supresses that index,
      # thus we have to expand then squeeze.  Resize returns float32 in the
      # range [0, uint8_max]
      image = tf.expand_dims(image, 0)
      image = tf.image.resize_bilinear(
          image, [height, width], align_corners=False)
      image = tf.squeeze(image, squeeze_dims=[0])
      image = tf.cast(image, dtype=tf.uint8)
      return image

    images_str_tensor = features["image"]
    images = tf.map_fn(
        decode_and_resize, images_str_tensor, back_prop=False, dtype=tf.uint8)
    images = tf.image.convert_image_dtype(images, dtype=tf.float32)
    images = tf.subtract(images, 0.5)
    images = tf.multiply(images, 2.0)

    image_id = features["image_id"]
    return image_id, images