A MULTI-PRIMARY CONVERSION

A method converts 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) have a valid range (VR) wherein their values occur. The N sub-pixels (SPi) emit light defined by N display primaries (DPi) of which at least four are independent. M resulting display primaries (RDi) are used (10) wherein a group of ones of the N display primaries (DPi) which are combined into a combined display primary (CDi) are replaced by the combined display primary (CDi). A first multi-primary conversion (MPC1) is performed (11) on the input pixel (IPi) to obtain resulting drive values (DRi) for the M resulting display primaries (RDi). It is checked (12) whether the M resulting drive values (DRi) have values in the valid range (VR). 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) the method allocates (12) a fixed value (FVi) to the resulting drive value (DRi) outside the valid range (VR), and selects (13) K out of the N display primaries (DPi). The selection includes the ones of the N display primaries (DPi) which were 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). The integer K is larger than 3. Finally the method performs (14) a second multi-primary conversion under a constraint (CO2) for the ones of the N display primaries (DPi) being combined into a combined display primary (CDi) in the first multi-primary conversion (MPC1).