081"></a><span class="lineno">   81</span>&#160;        <span class="comment">// TODO: Should this be concept-checked after &quot;if you remove const and reference&quot;? --mloskot</span></div><div class="line"><a name="l00082"></a><span class="lineno">   82</span>&#160;        <span class="keyword">using</span> reference = <span class="keyword">typename</span> D::reference; <span class="comment">// == PixelConcept (if you remove const and reference)</span></div><div class="line"><a name="l00083"></a><span 