import tensorflow as tf


    def validation_mapper(byte):
        image = tf.image.decode_jpeg(
            tf.reshape(byte, shape=[]), 3, **JPEG_OPT)
        image = resize_shortest_edge(image, tf.shape(image), 256)
        image = center_crop(image, 224)
        image = tf.reverse(image, axis=[2])  # to BGR
        return image

    def training_mapper(byte):
        jpeg_shape = tf.image.extract_jpeg_shape(byte)  # hwc
        bbox_begin, bbox_size, distort_bbox = tf.image.sample_distorted_bounding_box(
