Adobe 13102498 User Guide - Page 217

PHOTOSHOP CS3 210 User Guide 3 Drag the Radius slider or enter a value to determine the number of pixels surrounding the edge pixels that affect the sharpening. The greater the radius value, the wider the edge effects. And the wider the edge effects, the more obvious the sharpening. The Radius value varies according to the subject matter, the size of the final reproduction, and the output method. For high-resolution images, a Radius value between 1 and 2 is usually recommended. A lower value sharpens only the edge pixels, whereas a higher value sharpens a wider band of pixels. This effect is much less noticeable in print than on-screen, because a 2-pixel radius represents a smaller area in a high-resolution printed image. 4 Drag the Amount slider or enter a value to determine how much to increase the contrast of pixels. For highresolution printed images, an amount between 150% and 200% is usually recommended. 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 palette, 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 palette 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.