Patent ID: 8237751

Claim:
A method of converting an input pixel (IPi) defined by three values (ri, gi, bi) of input primaries (RI, GI, BI) into N drive values (DSi) for driving N sub-pixels (SPi) of a pixel (PIi) of a display device (DD), the N drive values (DSi) having a valid range (VR) wherein their values occur, the N sub-pixels (SPi) emitting light defined by N display primaries (DPi) of which at least four are independent, the method comprises: combining ones of the N display primaries (Dpi) into a combined display primary (CDi); replacing the ones of the N display primaries (Dpi) which are combined by the combined display primary (CDi) to obtain M resulting display primaries (RDi); performing a first multi-primary conversion (MPC 1 ), being a three to M multi-primary conversion, on the input pixel (IPi) to obtain resulting drive values (DRi) for the M resulting display primaries (RDi); checking whether the M resulting drive values (DRi) have values in the valid range (VR), and if the resulting drive value (DRi) of at least one of the M resulting display primaries (RDi) has a value outside the valid range (VR); allocating a fixed value (FVi) to the resulting drive value (DRi) outside the valid range (VR); selecting K out of the N display primaries (DPi), the selection including the ones of the N display primaries (DPi) being combined into a combined display primary (CDi) but not the display primaries (DPi) associated with the resulting drive value (DRi) outside the valid range (VR), wherein the integer K is larger than 3; and performing a second multi-primary conversion, being a three to K multi-primary conversion, under a constraint (CO 2 ) for the ones of the N display primaries (DPi) being combined into a combined display primary (CDi) in the first multi-primary conversion (MPC 1 ), the constraint (CO 2 ) being selected to decrease discontinuities at borders of gamuts defined by the K display primaries.