pan class="o">&gt;</span><span class="p">;</span>
  <span class="n">where</span> <span class="n">PixelIteratorConcept</span><span class="o">&lt;</span><span class="n">y_iterator</span><span class="o">&gt;</span><span class="p">;</span>
  <span class="n">where</span> <span class="n">x_coord_t</span> <span class="o">==</span> <span class="n">y_coord_t</span><span class="p">;</span>

  <span class="k">typename</span> <span class="n">coord_t</span> <span class="o">=</span> <span class="n">x_coord_t</span><span 