gros-motons.png is done with a double @convolve on a single list @redimmed in two different ways, (27 1) and (1 27). something like (-4 -3 -2 -1 0 1 2 3 4) or (-1 -2 -3 -4 0 4 3 2 1). brume.png is done in the same way with (1).