A method for transforming three color input signals (R, G, B) corresponding to three
gamut defining color primaries to four color output signals (R′, G′, B′, W) corresponding to the
gamut defining color primaries and one additional color primary W for driving a display having a
white point different from W includes the steps of: normalizing the color input signals (R,G,B) such that a combination of equal amounts in each
signal produces a color having XYZ tristimulus values identical to those of the additional color primary to produce normalized color signals (Rn,Gn,Bn); calculating a common
signal S that is a function F1 of the three normalized color signals (Rn,Gn,Bn); calculating a function F2 of the common
signal S and adding it to each of the three normalized color signals (Rn,Gn,Bn) to provide three color signals (Rn′,Gn′,Bn′); normalizing the three color signals (Rn′,Gn′,Bn′) such that a combination of equal amounts in each signal produces a color having XYZ tristimulus values identical to those of the display
white point to produce three of the four color output signals (R′,G′,B′); and calculating a function F3 of the common signal S and assigning it to the fourth color output signal W.