Patent ID: 7956877

Claim:
A method of converting a three-primary color input signal comprising a first, a second, and a third input signal (C 1 , C 2 , C 3 ) into a four-primary color drive signal comprising a first, second, third, and fourth drive signal (P 1 , P 2 , P 3 , P 4 ) for driving four primary colors of a multi-primary color additive display ( 3 ), the method comprises: defining three functions (F 1 , F 2 , F 3 ) representing the first, second, and third drive signal (P 1 , P 2 , P 3 ) as a function of the fourth drive signal (P 4 ), each one of the three functions (F 1 , F 2 , F 3 ) being defined by the three-primary color input signal and coefficients defining a dependence between the primary colors associated with the first, second and third drive signals (P 1 , P 2 , P 3 ) and the primary color associated with the fourth drive signal (P 4 ); determining intersection values (P 4 i ) of the fourth drive signal (P 4 ) at a set of intersections of: the three functions (F 1 , F 2 , F 3 ) mutually, and of the three functions (F 1 , F 2 , F 3 ) and a line (F 4 ) defined by the fourth drive signal (P 4 ) being equal to itself, wherein only the intersection values (P 4 i ) of functions having opposite signs of their first derivative are relevant; determining boundary values (P 4 min, P 4 max) of a valid range (VR) of values of the fourth drive signal (P 4 ), in which valid range (VR) all drive signals (P 1 , P 2 , P 3 , P 4 ) have valid values; determining calculated values (CV 1 , CV 2 , CV 3 ) of the first, second and third drive signals (P 1 , P 2 , P 3 ) at the intersection values (P 4 i ) and the boundary values (P 4 min, P 4 max); selecting a maximum value (Vmax) or minimum value (Vmin) of the calculated values (CV 1 , CV 2 , CV 3 ) at each one of the intersection values (P 4 i ) and each one of the boundary values (P 4 min, P 4 max); and selecting the intersection value (P 4 i ) or the boundary value (P 4 min, P 4 max) at which the maximum value (Vmax) or minimum value (Vmin) is minimum or maximum, respectively.