Real World Adobe Photoshop CS2: Industrial-strength Production Techniques

Unsharp Mask is the Swiss Army Knife of sharpening tools, but it's not the only way to sharpen images. One technique that we often use, particularly when sharpening for output, is to make a duplicate layer, using the techniques we described earlier in this chapter under "Sharpening Layers." But rather than setting the blending mode to Luminosity and running Unsharp Mask, we use one of the contrast-increasing blending modes such as Soft Light or Hard Light, then we run the High Pass filter on the layer.

High-Pass Sharpening

The High Pass filter (in the Other submenu, under the Filter menu) is a simple way to create an edge mask, but in this case we don't use it as a layer mask. Instead, we simply create a duplicate of the background layer (or create a new merged layer if we have more than one layer in the Layers palette), apply the High Pass filter to it, and then set the layer's blending mode to Soft Light or Hard Lightwhich increases the contrast around the edges, effectively sharpening the image.

As with the other layer-based sharpening techniques, you can use a whole bag of tricks to refine the sharpeninglike blurring noise in the mask, or painting on the layer itself with 50-percent gray (the neutral color for both the Hard Light and Soft Light blending modes) to erase the sharpening in local areas. You can apply a layer mask to confine the sharpening to a specific area, and you can stack multiple sharpening layers to apply selective sharpening to different areas of the image.

The critical parameter in using this technique is the Radius setting for the High Pass filter. If it's too small, you'll get little or no sharpening. If it's too big, grain and noise will appear in the image as if by some evil magic. However, for optimum output sharpening, we often need to produce a result that appears very ugly on screen (see the sidebar, "Sharpening and the Display," earlier in this chapter). Figure 9-16 shows the application of this technique and the resulting imageit looks fine in print, but the onscreen appearance is downright scary! When you look at the actual pixels on screen, bear in mind the size at which they'll reproduce in printa 6-pixel-wide halo, with 3 pixels in the light contour, and 3 in the dark, will produce an "ideal" sharpening halo when you print at 300 ppi, even if it looks downright hideous on screen. The only way to really judge print sharpness is to make a print!

On soft subjects and skin tones, Hard Light can give too strong a sharpening effect. On these types of image, or in any case where we want a more gentle sharpening effect, we often use Soft Light instead of Hard Light to avoid oversharpening the skin texture, as shown in Figure 9-17. You can switch between Hard Light and Soft Light after running the High Pass filter to see which rendering you prefer.