1. A method of redistributing an N-primary color input signal (IS) having a particular number ≧4 (N) of input components (I 1 ,. .. , IN) into N-primary color output signal (OS) having the particular number (N) of output components (P 1 ,. .. , PN) under a constraint (CON 2 ), the method comprising: defining, via a multi-primary redistribution conversion unit (MPRC), three functions (F 1 , F 2 , F 3 ) representing (i) three (P 1 , P 2 , P 3 ) of the output components (P 1 ,. .. , PN) as a function of (ii) the remaining N-3 output components (P 4 ,. .. , PN), wherein the functions (F 1 , F 2 , F 3 ) define ranges of possible values of three input components of the N-primary color input signal; substituting, via the multi-primary redistribution conversion unit (MPRC) and a primary color parameter unit (PCP), the values of the N input components (I 1 ,. .. , IN) into the three functions (F 1 , F 2 , F 3 ) to determine unknown coefficients (P 1 ′, P 2 ′, P 3 ′) of the three functions (F 1 , F 2 , F 3 ); and determining, via the multi-primary redistribution conversion unit (MPRC) and a constraint unit, optimal values of the N output components (P 1 ,. .. , PN) by (a) applying the constraint (CON 2 ) to the three functions (F 1 , F 2 , F 3 ), wherein the constraint (CON 2 ) comprises (a)(i) an equal luminance drive constraint or (a)(ii) a minimum/maximum drive constraint, wherein the equal luminance drive constraint determines selection of drive values of the N output components (P 1 ,. .. , PN) (a)(i)(1) defined by a linear combination of a first subset of the N output components that represents luminance of the first subset of output components and by a linear combination of a second subset of the N output components that represents luminance of the second subset of output components, and (a)(i)(2) subtraction of the linear combination of the second subset from the first subset is zero, wherein the minimum/maximum drive constraint determines selection of drive values of the N output components (P 1 ,. .. , PN) for which (a)(ii)(1) a maximum drive value is a minimal value or (a)(ii)(2) a minimum drive value is a maximum value, and (b) selecting an optimal value for each respective output component within a valid range (VS) which fits the equal luminance or minimum/maximum drive constraint, wherein the valid range (VS) comprises a common range of a respective N-3 output component (P 4 ,. .. , PN) for which all three functions (F 1 , F 2 , F 3 ) have values which are in the common range, and wherein the optimal values of the N output components (P 1 ,. .. , PN) are (i) determined in a single step, or (ii) first the optimal values of the N-3 output components (P 4 ,. .. , PN) are determined and then, using the optimal values of the N-3 output components (P 4 ,. .. , PN) in the three functions (F 1 , F 2 , F 3 ), the optimal values of the three output components are determined.