Method for transforming three colors input signals to four or more color signals

A method for transforming input signals (R, G, B) corresponding to three gamut defining color primaries to output signals (R', G', B', W) corresponding to the gamut defining color primaries and one additional color primary W for driving a display having emitters that emit light corresponding to the four color output signals including calculating a common signal value S as a function F1 of the input signals (R,G,B) for a current and neighboring pixels; determining a final common signal value S' based upon the common signals for the current and neighboring pixels; calculating the three color signals (R',G',B') by calculating a value of a function F2 of the final common signal value S' and adding it to each of the three color input signals (R,G,B); and calculating the output signal W as a function F3 of the final common signal value S'.