const</span> RedChannel&amp; red, <span class="keyword">const</span> GreenChannel&amp; green, <span class="keyword">const</span> BlueChannel&amp; blue) {
<a name="l00091"></a>00091     <span class="keywordflow">return</span> rgb_to_luminance_fn&lt;RedChannel,GreenChannel,BlueChannel,
<a name="l00092"></a>00092                                <span class="keyword">typename</span> channel_traits&lt;GrayChannel&gt;::value_type&gt;()(red,green,blue);
<a name="l00093"></a>00093 }
<a name="l00094"></a>00094 
<a na