In motion compensated interpolation of TV-pictures it is usual to divide the picture into a plurality of blocks, a motion vector being determined for each block. This division into blocks has the disadvantage, that sometimes block boundaries become visible (dirty window effect). The invention generates a continuous vector field from the blocked vector field with the aid of a median filter which calculates for each subblock (H1) from a number of subblocks (H1 . . . H4) into which each block (H) is divided, a motion vector based on the motion vectors of the original block (H) to which the subblock belongs, and of the original blocks (E, G) adjacent to the subblock (H1) concerned.