lass="keywordtype">void</span> check_gray() {  BOOST_STATIC_ASSERT((is_same&lt;typename Layout::color_space_t, gray_t&gt;::value)); }
<a name="l00146"></a>00146     <span class="keyword">template</span> &lt;<span class="keyword">typename</span> Channel&gt; <span class="keywordtype">void</span> assign(<span class="keyword">const</span> Channel&amp; chan, mpl::false_)       { check_gray(); at_c&lt;0&gt;(*this)=chan; }
<a name="l00147"></a>00147     <span class="keyword">template</span> &lt;<span class="keywor