Patent ID: 8428132

Claim:
A method for coding pictures in field or frame mode, the picture frame mode being able to use the field mode locally in the picture, for a group of macroblocks, the method comprising: calculating, for a group of macroblocks in field mode, spatial activities of each constituent macroblock and a temporal activity between the macroblocks of each constituent field, calculating an activity index relating to the group that is an increasing function of the temporal activity and a decreasing function of the calculated spatial activities, comparing the activity index relating to the group, to a predefined threshold, to define it as a group having activity, coding the picture in field or frame mode according to a number of macroblock groups detected having activity with respect to a number of groups of macroblocks in the picture, wherein said group is a supermacroblock and wherein the activity index equals to R = FLADInterMB 1 + FLADIntraMB n + FLADIntraMB n - 1 with FLABInterMB = ∑ j = 0 15 ⁢ ∑ i = 0 15 ⁢  FY n ⁡ ( i , j ) - FY n - 1 ⁡ ( i , j )  , ⁢ FLADIntraMB n = ∑ j = 0 7 ⁢ ∑ i = 0 15 ⁢  FY n ⁡ ( i , 2 ⁢ ⁢ j ) - FY n ⁡ ( i , 2 ⁢ ⁢ j + 1 )  , being an inter-field luminance gradient; being an intra-field luminance gradient in field n; and FY n (i,j) representing the luminance value of the pixel of horizontal coordinate i and vertical coordinate j of the field n of the supermacroblock.