I read in the documentation on the colour calibration module that in bypass mode, the R,G and B tabs act like a channel mixer with a matrix multiplication.
┌ R_out ┐ ┌ Rr Rg Rb ┐ ┌ R_in ┐
│ G_out │ = │ Gr Gg Gb │ X │ G_in │
└ B_out ┘ └ Br Bg Bb ┘ └ B_in ┘
I wanted to experiment changing a purple into green . With 9 variables and 3 equations, there are many possible 3x3 matrices that will do the job. I wanted to change the colour (152,155,159) into (69,203,129) so I just took the matrix
┌ 69/152 0 0 ┐
│ 203/152 0 0 │
└ 129/152 0 0 ┘
I understand that I am using output values taken with the colour picker instead of the values from the working space but the behaviour of the module surprised me.
Then I just checked if by entering 0.33 in the columns of red and 0 everywhere else would turn my red patch into grey. Nope !
Am I getting my maths wrong, putting the coefficients in the wrong place or is this channel mixer not just a matrix multiplication ?
Thanks for any help,