490         <span class="keyword">typedef</span> <span class="keyword">typename</span> mpl::if_c&lt;is_mutable, ref_t, value_type&gt;::type           reference;
<a name="l00491"></a>00491         <span class="keyword">typedef</span> reference                                                         result_type;
<a name="l00492"></a>00492 
<a name="l00493"></a>00493         <a class="code" href="g_i_l_0513.html" title="Function object that returns a grayscale reference of the K-th channel (specified...">kth_c