frame mode coding method or frame

The method comprises the steps of: - calculating the spatial activity of each macroblock and the temporal activity between the macroblocks constituting a group of macroblocks in field mode, - calculating a relative activity index of the group which is a increasing function of the temporal activity and a decreasing function of the spatial activity of the group, - comparison (10) of the index of relative activity of the group to a predefined threshold to define it as a group activity with (11), - encoding the image in field or frame mode (15, 16) depending on the number of the detected macroblocks groups with activity (14) relative to the number of macro blocks in the groups image.Les applications include data compression in particular the H.264 standard