pan>

            <span class="c1">#rgbc = np.ones(rgbc.shape)*rgbc.mean() # test if eew ends up at origin</span>
            
            <span class="c1"># calculate achromatic and color difference signals, A, a, b:</span>
            <span class="n">Aab</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">dot</span><span class="p">(</span><span class="n">MAab</span><span class="p">,</span> <span class="n">rgbc</span><span class="o">.</span><span class="n">T</sp