title: How is the Laplacian used for Unsharp Mask?
body: <p>Matlab's <em>fspecial</em> unsharp mask uses a Laplacian kernel to achieve sharpening of the image.</p>
  
  <p>From what I know, the image needs to be blurred first, and then the blurred image is subtracted from the original to get a sharper image. The Laplacian part comes exactly where alleged smoothing should take place. Correct me if I'm wrong, but Laplacian doesn't do any smoothing.</p>
  
  <p>So how does the Laplacian help in sharpening the image?</p>