Patent ID: 8199831

Claim:
A method for coding the video level of a current pixel of a colour component of a picture to be displayed on a display device into a code word belonging to at least a first code set or a second code set or both, the second code set being a subset of the first code set, the code words of the second code set being selected among the code words of the first code set according to the rule that the temporal centre of gravity for the light generation of the corresponding sub-field code words grows continuously with the video level of said code words by selecting certain levels, with an exception in which the temporal centre of gravity does not grow continuously in the low video level range up to a first predetermined number of low level code words or in the high video level range from a second predetermined number of high level code words or in both, comprising: determining, by an adaptive coder, for a predetermined number of neighbouring pixels belonging to a window including said current pixel, at least a first floor level and a first ceiling level that can be coded by a code word of the first code set and a second floor level and a second ceiling level that can be coded by a code word of the second code set, the first and second floor levels being respectively the highest video level among the video levels corresponding to the code words of the first and second code sets equal to or lower than the video level of the current pixel and the first and second ceiling levels being respectively the lowest video level among the video levels corresponding to the code words of the first and second code sets equal to or higher than the video level of the current pixel, determining, for said current pixel, the minimum level between the first floor level of said current pixel and the ceiling levels of said predetermined number of neighbouring pixels of the window including the current pixel and determining for said current pixel the maximum level between the first ceiling level of said current pixel and the floor levels of said predetermined number of neighbouring pixels, said minimum level being called floor level of the current pixel and said maximum level being called ceiling level of the current pixel, substituting, for said current pixel, the floor level by the second floor level if the said floor level is lower than the second floor level and the ceiling level by the second ceiling level if said ceiling level is higher than the second ceiling level, and selecting, for said current pixel, the code word among the code word of the floor level and the code word of the ceiling level according to dithering for coding the video level of the current pixel.