\(\begin{align} K &= 1-\max(R,G,B)\\ C &= \frac{1-R-K}{1-K}\\ M &= \frac{1-G-K}{1-K}\\ Y &= \frac{1-B-K}{1-K} \end{align}\)
\(\begin{align} R &= (1-C)(1-K)\\ G &= (1-M)(1-K)\\ B &= (1-Y)(1-K) \end{align}\)