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Chapter 10. Sharpening: Getting an Edge ... > How the Unsharp Mask Filter Works

How the Unsharp Mask Filter Works

The Unsharp Mask filter operates pixel by pixel, which explains why it takes so long, even on a very fast machine. It compares each pixel to its neighbors, looking for a certain amount of contrast between adjacent pixels—which it assumes is an edge. It then increases the contrast between those pixels according to the parameters you set. This creates a halo that, at normal viewing distances, increases apparent sharpness.


  

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