class_docstr: Base class for problems with images.
class_docstr_tok: ["Base","class","for","problems","with","images","."]
code: def preprocess_example(self, example, mode, hparams):
      if not self._was_reversed:
          example["inputs"] = tf.image.per_image_standardization(
              example["inputs"]
          )
      return example
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import io
  import os
  import numpy
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.layers import common_layers
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import contrib
  from tensor2tensor.utils import metrics
  import tensorflow.compat.v1
label_desc: Use image node_id 4 for calling the ImageProblem obj's underlying member method code with example usage: obj.preprocess_example(example, mode, hparams) and returns: example