Redistribution of N-primary color input signals into N-primary color output signals

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.

2. The method of redistributing as claimed in claim 1 , wherein the redistributing occurs in a linear light domain, and wherein the defining three functions (F 1 , F 2 , F 3 ), via the multi-primary redistribution conversion unit (MPRC), defines three linear functions.

3. The method of redistributing as claimed in claim 2 , wherein the defining the three functions (F 1 , F 2 , F 3 ), via the multi-primary redistribution conversion unit (MPRC), defines the three linear functions (F 1 , F 2 , F 3 ) as

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wherein P 1 to PN are the N primary color output signals, the unknown coefficients are input signal dependent coefficients P 1 ′, P 2 ′, P 3 ′ which correspond to three input components (I 1 , I 2 , I 3 ) when the output component(s) P 4 to PN are zero, and matrix coefficients ki,j are predefined by a dependency between (i) three primary colors associated with the three output components P 1 to P 3 , and (ii) N-3 other primary colors associated with the N-3 output component(s) P 4 to PN; and

the substituting the values of the N input components (I 1 , . . . , IN) into the three functions (F 1 , F 2 , F 3 ) to determine coefficients (P 1 ′, P 2 ′, P 3 ′) of the three functions (F 1 , F 2 , F 3 ), via the multi-primary redistribution conversion unit (MPRC) and the primary color parameter unit (PCP), provides the input signal dependent coefficients (P 1 ′, P 2 ′, P 3 ′).

4. The method of redistributing as claimed in claim 2 , wherein the determining the optimal values, via the multi-primary redistribution conversion unit (MPRC) and the constraint unit, comprises at least adding a further equation to the three equations to obtain an extended set of equations, and determining a solution of the output components (P 1 , . . . , PN) for the extended set of equations.

5. The method of redistributing as claimed in claim 2 , wherein a further equation defines a linear combination between at least a first subset of the N output components (P 1 , . . . , PN) and a second subset of the N output components (P 1 , . . . , PN).

6. 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 (MPRC) three functions (F 1 , F 2 , F 3 ) representing three (P 1 , P 2 , P 3 ) of the output components (P 1 , . . . , PN) as a function of the remaining N-3 output components (P 4 , . . . , PN);

substituting (MPRC) the values of the 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 (MPRC) optimal values of the output components (P 1 , . . . , PN) by applying the constraint (CON 2 ) to the three functions (F 1 , F 2 , F 3 ), wherein the redistributing occurs in a linear light domain, and wherein the defining three functions (F 1 , F 2 , F 3 ) defines three linear functions, and wherein N=4, and wherein the N-primary color output signal (OS) comprises a first, second, third, and fourth output component (P 1 , P 2 , P 3 , P 4 ) for driving four primary colors of a multi-primary color additive display, wherein

the defining the three functions (F 1 , F 2 , F 3 ), defines three functions representing the first, second, and third output component (P 1 , P 2 , P 3 ) as a function of the fourth output component (P 4 ), and wherein the determining (MPRC) the optimal values further comprises:

determining intersection values (P 4 i ) of the fourth output component (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,

calculating associated first, second and third output components (P 1 , P 2 , P 3 ) at the intersection values (P 4 i ) of the fourth output component (P 4 ), and at boundary values (P 4 min, P 4 max) of a valid range (VR) of the fourth output component (P 4 ) wherein all output components (P 1 , P 2 , P 3 , P 4 ) have valid values, to obtain calculated values (CV 1 , CV 2 , CV 3 ),

determining values of interest (CV 1 , CV 2 , CV 3 , P 4 i ) comprising the intersection values (P 4 i ) and the boundary values (P 4 min, P 4 max) and the associated calculated values (CV 1 , CV 2 , CV 3 ),

selecting a maximum value (Vmax) or minimum value (Vmin) of the values of interest (CV 1 , CV 2 , CV 3 , P 4 i ) at the intersection values (P 4 i ) and 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.

7. A method of driving a display device having sets of N sub-pixels, the method comprising:

converting, via a multi-primary conversion unit (MPC), a three-primary input signal (R, G, B) into an N-primary color input signal (IS) under a first constraint (CON 1 ); and

redistributing, via a multi-primary redistribution conversion unit (MPRC), the N-primary color input signal (IS) into the N-primary color output signal (OS) under a constraint (CON 2 ) in accordance with claim 1 , wherein the constraint mentioned in claim 1 is a second constraint (CON 2 ).

8. The method of driving a display device as claimed in claim 7 , wherein, if the first constraint (CONI) and the second constraint (CON 2 ) cannot be satisfied simultaneously, the method further comprises defining, via the multi-primary redistribution conversion unit (MPRC), an adapted second constraint being defined by a linear combination of solutions associated with the first constraint (CON 1 ) and the second constraint (CON 2 ).

9. A non-transitory computer readable medium embodied with a computer program comprising processor readable code to enable a processor to execute the method of claim 1 , the processor readable code comprising:

code for defining three functions (F 1 , F 2 , F 3 ) representing three of the N-primary color output components as a function of the remaining N-3 primary color output signal components;

code for substituting the values of the primary color input components into the three functions to determine unknown coefficients of the three functions; and

code for determining optimal values of the N-primary color output signal by applying the constraint to the three functions.

10. The non-transitory computer readable medium as claimed in claim 9 , wherein the computer readable medium is a software plug-in in an image processing application.

11. A system for redistributing a N-primary color input signal (IS) having N input components into a N-primary color output signal having N output components (P 1 , . . . , PN) under a constraint, the system comprises:

means for defining three functions (F 1 , F 2 , F 3 ) representing (i) three of the N-primary color output components as a function of (ii) the remaining N-3 primary color output signal components, wherein the defining means comprises a multi-primary redistribution conversion unit, and 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;

means for substituting the values of the N primary color input components into the three functions to determine unknown coefficients of the three functions, wherein said substituting means comprises the multi-primary redistribution unit and a primary color parameter unit; and

means for determining optimal values of the N output components of the N-primary color output signal by (a) applying the constraint to the three functions, wherein the constraint 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 (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 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, wherein the determining means comprises the multi-primary redistribution conversion unit and a constraint unit.

12. A display apparatus comprising the system of claim 11 , a signal processor for receiving an input signal representing an image to be displayed to supply the N input components (I 1 , . . . , IN) to the system, and a display device for supplying the N output components (P 1 , . . . , PN) to sub-pixels of the display device.

13. A camera comprising the system of claim 11 , and an image sensor supplying the N-primary color input signal (IS).

14. A portable device comprising the display apparatus of claim 12 .