code: def call(self, inputs):
      return tf.reduce_sum(inputs, axis=-1, keepdims=True)
  
imports: import logging
  import numpy
  from dipy.data import get_fnames
  from dipy.testing.decorators import doctest_skip_parser
  from dipy.utils.optpkg import optional_package
  from dipy.align.reslice import reslice
  from dipy.nn.utils import normalize, set_logger_level, transform_img
  from dipy.nn.utils import recover_img, correct_minor_errors
label_desc: Use image node_id 2 for calling the ChannelSum obj's underlying member method code with example usage: obj.call(inputs) and returns: tf