de/>vl_demo_frame</code>.
  </span>
 </div>
</div>

<p>Note that, when features extracted by a detector such
as <code/>vl_covdet</code> or <code/>vl_sift</code>, are normalized, this
is done by applying the affine transformation which is
the <em>inverse</em> of the one specified by the feature frame; in
this way, in fact, the frame is transformed back to its standardized
version.</p>

<p>Similarly, unoriented frames can all be seen as affine
transformations of the standard unoriented frame (the unit circle
