Fotoxx Sharpen Tools
   1. Original image
   2. Blurred image, blur radius 3
   3. Unsharp Mask - a common method, very effective but prone to creating "halos" around high-contrast edges.
   4. Gradient - pixel brightness gradients are steepened locally. Halo effect is reduced.
   5. Kuwahara - strong edges are made very sharp, weak edges are wiped out. No halos. Some loss of detail.
   6. Median Difference - pixel brightness changed in proportion to brightness / (median neighborhood brightness). No halos.