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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _normalize(image):
 """Normalize the image to zero mean and unit variance."""

  offset = tf.constant(MEAN_RGB, shape=[1, 1, 3])
  image -= offset

  scale = tf.constant(STDDEV_RGB, shape=[1, 1, 3])
  image /= scale
  return image