title: tf.image.pad_to_bounding_box VS tf.pad and tf.image.crop_to_bounding_box VS tf.slice
body: <p>I'd like to understand why does the two functions <code>tf.image.crop_to_bounding_box</code> and <code>tf.image.pad_to_bounding_box</code> exists, since the behaviour of these two functions can be done really simply with respectively <code>tf.slice</code> and <code>tf.pad</code>.</p>
  
  <p>They are not so much easier to understand, and their scope is narrow since they accept only 3D and 4D tensors. Furthermore, they tend to be slower in terms of time of execution. </p>
  
  <p>Is there something I miss here ? </p>