Using the Unsharp Mask filter

The first thing you need to know about the Unsharp Mask filter is that it has a weird name. The filter has nothing to do with unsharpening — whatever that is — nor is it tied into Photoshop's masking capabilities. Unsharp Mask is named after a traditional film compositing technique (which is also oddly named) that highlights the edges in an image by combining a blurred film negative with the original film positive.

That's all very well and good, but the fact is most Photoshop artists have never touched a stat camera (an expensive piece of machinery, roughly twice the size of a washing machine, used by image editors of the late Jurassic, pre-Photoshop epoch).

Even folks like me who used to operate stat cameras professionally never had the time to delve into the world of unsharp masking. In addition — and much to the filter's credit — Unsharp Mask goes beyond traditional camera techniques.

To understand Unsharp Mask — or Photoshop's other sharpening filters, for that matter — you first need to understand some basic terminology. When you apply one of the sharpening filters, Photoshop increases the contrast between neighboring pixels. The effect is similar to what you see when you adjust a camera to bring a scene into sharper focus.

Two of Photoshop's sharpening filters, Sharpen and Sharpen More, affect whatever area of your image is selected. The Sharpen Edges filter, however, performs its sharpening operations only on the edges in the image — those areas that feature the highest amount of contrast.

Unsharp Mask gives you both sharpening options. It can sharpen only the edges in an image or it can sharpen any portion of an image according to your exact specifications, whether it finds an edge or not. It fulfills the exact same purposes as the Sharpen, Sharpen Edges, and Sharpen More commands, but it's much more versatile. Simply put, the Unsharp Mask tool is the only sharpening filter you'll ever need.

When you choose Filter ^ Sharpen ^ Unsharp Mask, Photoshop displays the Unsharp Mask dialog box, shown in Figure 10-7, which offers the following options:

4 Amount: Enter a value between 1 and 500 percent to specify the degree to which you want to sharpen the selected image. Higher values produce more pronounced effects.

Figure 10-7: Despite any conclusions you may glean from its bizarre name, the Unsharp Mask filter sharpens images according to your specifications in this dialog box.

* Radius: This option determines the thickness of the sharpened edge. Low values produce crisp edges. High values produce thicker edges with more contrast throughout the image.

* Threshold: Enter a value between 0 and 255 to control how Photoshop recognizes edges in an image. The value indicates the numerical difference between the brightness values of two neighboring pixels that must occur if Photoshop is to sharpen those pixels. A low value sharpens lots of pixels; a high value excludes most pixels from the running.

The preview options offered by the Unsharp Mask dialog box are absolutely essential visual aids that you're likely to find tremendously useful throughout your Photoshop career. Just the same, you'll be better prepared to experiment with the Amount, Radius, and Threshold options and less surprised by the results if you read the following sections, which explain these options in detail and demonstrate the effects of each.

Photoshop Secrets

Photoshop Secrets

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