Illustration of how the direction of anisotropy changes with respect to contour size. A yellowish contour with “radius” (defined in the figure as the horizontal pixel distance from the center) of ∼20 is selected, and the direction of anisotropy for this contour is shown by a yellow arrow. One can pick a bigger contour (e.g., the reddish one we picked with “radius” of ∼60); the direction of anisotropy for this contour is changed significantly.