8 x NUMKEYPOINTS matrix with one
descriptor per column, in the same format of <a href="%pathto:vl_sift;">VL_SIFT</a>().
</p><p>
<a href="%pathto:vl_dsift;">VL_DSIFT</a>() does NOT compute a Gaussian scale space of the image
I. Instead, the image should be pre-smoothed at the desired scale
level, e.b. by using the <a href="%pathto:vl_imsmooth;">VL_IMSMOOTH</a>() function.
</p><p>
The scale of the extracted descriptors is controlled by the option
SIZE, i.e. the width in pixels of a spatial bin (recall that a
