n><span class="o">**</span><span class="mf">0.5</span><span class="p">)</span>

            <span class="c1"># calculate brightness Q:</span>
            <span class="n">Q</span> <span class="o">=</span> <span class="n">cA</span><span class="o">*</span><span class="p">(</span><span class="n">A</span> <span class="o">+</span> <span class="n">cHK</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">*</span><span class="n">M</span><span class="o">**</span><span class="