DIFFERENCE

{@usesMathJax} Subtracts darker from lighter with higher contrast.

\begin{equation} \alpha_{out} = \alpha_{src} + \alpha_{dst} - \alpha_{src} * \alpha_{dst} \end{equation}

\begin{equation} C_{out} = C_{src} + C_{dst} - 2 * min(C_{src} * \alpha_{dst}, C_{dst} * \alpha_{src}) \end{equation}