Monday, June 30, 2008
For the best image quality, focus your sharpening on the areas that need it most
In fact, if a photo has out-of-focus areas in it, overall sharpening can cause unneeded problems. Sharpening affects tonal details. It enhances the difference in tone at the edges of objects and other features of a scene so that they appear sharper. Yet out-of-focus areas have differences in tone, too-differences that look their best if not changed. Plus, if there's noise in a photo, it's almost always in out-of-focus areas. Overall sharpening, then, will intensify that noise. This is a problem with using Smart Sharpen in Photoshop, since this control doesn't have a Threshold setting. Threshold in Unsharp Mask affects small details, especially noise, so without it, Smart Sharpen tends to overemphasize noise.
Sharpen What's Sharp
The logical step is to limit sharpening to the sharply focused parts of a photo. You know what should be sharp in your photo and what's out of focus. Sharpen what's sharp, and leave the rest alone.
You can do this by selecting around your sharp areas, feathering the selection and applying your sharpening adjustment. Either Unsharp Mask or Smart Sharpen then will work only within the selected area. This selection can be made quickly and effectively with CS3's new Quick Selection Tool (and you don't need to feather it if you set the hardness at a low value). This tool has been part of Photoshop Elements for a while.
A better way to selectively sharpen a photo is to sharpen to a layer.
Using A Layer
To sharpen to a layer, duplicate your original image as a new layer. This, in effect, is a stack of two unsharpened photographs-one on top of the other. The easiest way to do this in Photoshop or Photoshop Elements is to use the Ctrl/Cmd + J keyboard command. You'll see the stack in the Layers palette.
You must have pixels in order to sharpen, so you can't do this quick layer copy trick if you have multiple adjustment layers. However, you can click on your top layer and hold down these modifier keys: Alt/Option + Shift + Ctrl/Cmd. With these held down, press E. This combines all of your layers and adjustments into one new pixel layer and puts it on top of the stack. If you have an older version of Photoshop, you may have to press N before E.
Now sharpen the top layer. There are many formulas for sharpening, and as long as they don't oversharpen a photo, they all work. The reason for the differences is that photographers have different goals for a photograph. A baby is sharpened much differently than a detailed bit of architecture, for example.
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