> implements a Gaussian scale space, a data structure representing an image at multiple resolutions <a class="el" href="citelist.html#CITEREF_witkin83scale-space">[33]</a> <a class="el" href="citelist.html#CITEREF_koenderink84the-structure">[13]</a> <a class="el" href="citelist.html#CITEREF_lindeberg94scale-space">[14]</a> . Scale spaces have many use, including the detection of co-variant local features <a class="el" href="citelist.html#CITEREF_lindeberg98principles">[15]</a> such as SIFT, Hessian-Affine, 