code: def test_png_format_roundtrip(self):
      images = self._generate_images(c=1)
      pb = self.image("mona_lisa", images)
      encoded = pb.value[0].tensor.string_val[2]  # skip width, height
      self.assertAllEqual(images[0], tf.image.decode_png(encoded))
  
imports: import glob
  import os
  import numpy
  import tensorflow
  from tensorboard.compat import tf2
  from tensorboard.compat.proto import summary_pb2
  from tensorboard.plugins.image import metadata
  from tensorboard.plugins.image import summary
label_desc: Use image node_id 6 for calling the SummaryBaseTest obj's underlying member method code with example usage: obj.test_png_format_roundtrip() without return types