1. A method for processing at least a part of a colour picture comprising at least one pixel defined by a plurality of colour values, each colour value being variable between black and a colour clip value, with the following steps: determining the lowest of the colour clip values as common clip value, determining for each colour value the quantity of the colour value above the common clip value, computing a linear combination of said quantities, for at least one of the colour values, outputting as processed colour value: the colour value plus said linear combination if said colour value is below the common clip value; the common clip value plus said linear combination if said colour value is above the common clip value.