def encode_images_as_png(images):
  """Yield images encoded as pngs."""
  if tf.executing_eagerly():
    for image in images:
      yield tf.image.encode_png(image).numpy()
  else:
    (height, width, channels) = images[0].shape
    with tf.Graph().as_default():
      image_t = tf.placeholder(dtype=tf.uint8, shape=(height, width, channels))
      encoded_image_t = tf.image.encode_png(image_t)
      with tf.Session() as sess:
        for image in images:
          enc_string = sess.run(encoded_image_t, feed_dict={image_t: image})
          yield enc_string