class_docstr: Base class for all image preprocess ops.
class_docstr_tok: ["Base","class","for","all","image","preprocess","ops","."]
docstr: Looks up the axis storing object instances for a given feature.
docstr_tok: ["Looks","up","the","axis","storing","object","instances","for","a","given","feature","."]
code: def _get_instance_axis(feature_key):
      """Looks up the axis storing object instances for a given feature."""
      if feature_key in FEATURES_WITH_FIRST_INSTANCE_AXIS:
          return 0
      elif feature_key in FEATURES_WITH_NO_INSTANCE_AXIS:
          return None
      else:
          raise ValueError(
              f"Please specify instance axis for feature key {feature_key}."
          )
  
imports: import abc
  import dataclasses
  from typing import Optional, Sequence, Tuple, Union
  from clu import preprocess_spec
  from scenic.projects.owl_vit.preprocessing import modalities
  from scenic.projects.owl_vit.preprocessing import transforms
  import tensorflow
label_desc: Use image node_id 4 for calling the ImagePreprocessOp obj's underlying member method code with example usage: obj._get_instance_axis(feature_key) and returns: int, None