|Errors in Image Intensity
This pattern is a black and white checkerboard with small squares placed in the corners of the black tiles near the edges. This creates the illusion of a wave in it.
The white squares change the type of edge that separates the tiles of the checkerboard. They create bars - there is a white area (from a little white square) next to a black bar (from a black checkerboard tile) next to a white area (from a white checkerboard tile). The edges at the boundaries of the bar (type 2 edges) drift apart under smoothing while the other edges between the black and white tiles (type 1 edges) stay in place.
The following picture is a closer look at the edge detection on the smoothed image of the Wave pattern.
The next set of pictures takes an even closer look and provides movement vectors that show how the edges move from their original positions.
To see the distortion more clearly, use the flash animation below.