A method is described which converts a three primary color input signal (Cx, Cy, Cz) into N drive signals (P1, . . . , PN) to drive N>3 primary colors of a multi-primary color display (3). The method determines (1) a valid range (VS) wherein the N drive signals (P1, . . . , PN) have valid values by performing the steps of (i) defining 3 functions representing 3 of the drive signals (P1, P2, P3) as a function of the remaining N−3 drive signal(s) (P4, . . . , PN), and (ii) calculating (1) a common range in a space formed by the N−3 drive signal(s) (P4, . . . , PN) wherein each one of the 3 functions has valid values. The method selects (2) a point from the common range to determine the N drive signals (P1, . . . , PN).