Adobe Photoshop CS4 - Manual (Page 223)

216 USING PHOTOSHOP CS4
Retouching and transforming
Last updated 1/10/2010
5 Drag the Threshold slider or enter a value to determine how different the sharpened pixels must be from the
surrounding area before they are considered edge pixels and sharpened by the filter. For instance, a threshold of 4
affects all pixels that have tonal values that differ by a value or 4 or more, on a scale of 0 to 255. So, if adjacent pixels
have tonal values of 128 and 129, they are not affected. To avoid introducing noise or posterization (in images with
flesh tones, for example), use an edge mask or try experimenting with Threshold values between 2 and 20. The
default Threshold value (0) sharpens all pixels in the image.
If applying Unsharp Mask makes already bright colors appear overly saturated, choose Edit > Fade Unsharp Mask
and choose Luminosity from the Mode menu.
Sharpen selectively
You can sharpen parts of your image by using a mask or a selection. This is useful when you want to prevent
sharpening in certain parts of your image. For example, you can use an edge mask with the Unsharp Mask filter on a
portrait to sharpen the eyes, mouth, nose, and outline of the head, but not the texture of the skin.
Using an edge mask to apply the Unsharp Mask only to specific features in an image
Sharpen a selection
1 With the image layer selected in the Layers panel, draw a selection.
2 Choose Filter > Sharpen > Unsharp Mask. Adjust the options and click OK.
Only the selection is sharpened, leaving the rest of the image untouched.
Sharpen an image using an edge mask
1 Create a mask to apply sharpening selectively. There are many ways to create an edge mask. Use your favorite
method, or try this one:
• Open the Channels panel and select the channel that displays the grayscale image with the greatest contrast in the
document window. Often, this is the green or the red channel.
Selecting a channel with the greatest contrast
• Duplicate the selected channel.
• With the duplicate channel selected, choose Filter > Stylize > Find Edges.