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Give yourself an edge by fine-tuning your sharpening skills

Added on Friday 27th of July 2007 02:20 am EST
 

Application:

Adobe Photoshop 7/CS/CS2

Operating Systems:

Macintosh, Microsoft Windows

 

 

Images often require some degree of sharpening, but sharpening the entire image can introduce unsightly noise. You can avoid this when you take the time to sharpen only the areas of the image that need it.

 

To fine-tune your sharpening skills, we’ll:

     Help you figure out what types of images benefit from this technique.

     Show you how to select just the edges in your image.

     Explain how to transform that selection into a mask so you can selectively sharpen just the edges.

 

 

You know you need to sharpen your images but sometimes sharpening has the adverse affect of generating noise in what was an otherwise smooth continuous tone. That’s when sharpening gets tricky. Should you sacrifice one portion of the image to improve the quality of another? If you follow this technique, you won’t have to sacrifice any part of your image quality. We’ll show you how to get sharp edges without the extra noise, as shown in Figure A.

 

A

 

Pick the right image

 

While you could apply this technique to any image, not all images will actually benefit from it. Since it takes a few extra steps than simply applying your favorite sharpening filter, it’s worth it to make sure your image truly needs it. So how can you tell? Use these tips:

        This technique works well on images with large areas of continuous tone—such as a sky or exposed skin—where noise is more likely to be introduced.

        This technique won’t benefit images that have a lot of detail with smaller areas of continuous tone. As you can see in Figure B, the rocks fare just fine when we apply a simple 3-pixel radius High Pass filter.

        If you aren’t sure if your image needs special sharpening treatment, apply a basic sharpening filter and review the results. If you notice a lot of new noise in your image, undo the sharpening command and proceed with this technique.

 

B

 

 

Make a mask

 

The trick to sharpening an image, but not introducing noise, is to target only those areas of the image that you wish to sharpen. We’ll show you how to create a mask that’s comprised of just the image’s edges.

 

To create a mask of the image’s edges:

1.       Select the Background layer and press [command]A ([Ctrl]A in Windows) to select it and then press [command]C ([Ctrl]C in Widows) to copy it.

2.      Go to the Channels palette and click on the Create A New Channel button new_channel at the base of the Channels palette to add a new channel.

3.      Press [command]V ([Ctrl]V in Windows) to paste the image into the channel as shown in Figure C.