Diagram of the location of the 25 bicubic B‐splines used to construct the convolution kernels. The 9 circles, 8 squares, and 8 hexagons mark the centers of the B‐spline maxima with widths of 1, ﹩\frac{3}{2}﹩, and 2 pixels, respectively. The dashed lines indicate the ﹩9\times 9﹩ grid of the underlying convolution kernels.