inaccurate linear equations solver in color checker module
The color checker module is based on three-dimensional interpolation using N radial non-linear basis functions plus three linear functions and a constant. Here, N denotes the number of color patches in the color checker. The N+4 interpolating coefficients are computed by solving a linear system of (N+4) equations for (N+4) unknowns. The current implementation of color checker module utilizes a routine to solve the linear system that becomes numerically unstable if the number of color patches in the color checker becomes small. This can lead to strong color shifts even if all target colors equal the source colors as indicated in the figures attached to this bug report.
The described bug has been fixed in pull request 1541.