Mahy and Delabastita [1996] show that Eq. (1) can be inverted by
relating it to a hexic polynomial whose roots determine the possible
values for αc. The remaining coefficients, αm and αy, are
then found through algebraic manipulation. The polynomial has up
to six solutions, so, the inverse of Eq. (1) is not uniquely defined,
which could result in non-smooth separations making the subsequent
dot shape fitting difficult. Some of these solutions might also
not be physically meaningful, e.g. by having a non-zero imaginary
component, or α < 0 or α > 1. In practice, however, this does
not seem an issue since for all scans we tried almost all non-black
pixels had a unique physically meaningful solution.