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Applying the Unsharp Mask Filter in Adobe Photoshop CS5

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In this excerpt from Photoshop CS5 for Windows and Macintosh: Visual QuickStart Guide, Elaine Weinmann and Peter Lourekas show you how to work with Amount, Radius, and Threshold in the Unsharp Mask filter.
From the book

To do its job of sharpening an image, the Unsharp Mask filter increases the contrast between adjacent pixels. You will need to choose three variables in the dialog: Amount, Radius, and Threshold.

To apply the Unsharp Mask filter

  1. Choose a zoom level of 50–100% for your image, then duplicate an image layer (Ctrl-J/Cmd-J).A
  2. Right-click the duplicate layer and choose Convert to Smart Object.
  3. With the Smart Object layer selected, choose Filter > Sharpen > Unsharp Mask. The Unsharp Mask dialog opens. Move it out of the way, if necessary, so the document is still in view.
  4. Choose an Amount percentage to control how much the contrast is increased. Use a low setting (try 80–100) for figures or natural objects or a higher setting (150–170) for sharp-edged objects. For a high-resolution image (2000 × 3000 pixels or higher), try an Amount of 130–170.B
    • Uncheck, then recheck Preview to compare the original and sharpened images. Choose a zoom level for the preview of 50–100%. To bring a different area of the image into view, either drag in the preview or click in the document.
  5. The Radius affects how many neighboring pixels around high-contrast edges the filter affects. When choosing an appropriate Radius, you need to consider the pixel count of the image and its subject matter.C The higher the pixel count, the higher the Radius value needed to achieve the desired result. For a low-contrast image that contains large, simple objects and smooth transitions, try a high Radius of 2 (you’ll rarely need to use a higher value), whereas for an intricate, high-contrast image containing many sharp transitions, try a lower Radius of around 1.

    Note: The Amount and Radius settings are interdependent, meaning if you raise the Radius, you’ll need to lower the Amount, and vice versa.

  6. Choose a Threshold value (0–255) to establish how different in value an area of pixels must be from a high-contrast edge to be affected by the filter (A, next page). Start with a Threshold value of 0 (to sharpen the entire image), then increase it slowly. At a Threshold of 5–10, high-contrast areas will be sharpened and areas of lesser contrast will be sharpened much less. When increasing the Threshold, you can also increase the Amount and Radius to sharpen the edges. Thankfully, the filter won’t oversharpen the low-contrast areas.
  7. Click OK.B To adjust the settings at any time, double-click the Unsharp Mask listing on the Layers panel.
    • If the sharpening produced color halos along the edges of the objects, choose Luminosity as the blending mode for the Smart Object layer. This will limit the sharpening to luminosity values and remove it from hue and saturation values.
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