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Want High Pass sharpening? Take it into the Lab

Added on Friday 27th of July 2007 02:23 am EST


Adobe Photoshop 7/CS/CS2

Operating Systems:

Macintosh, Microsoft Windows


I enjoyed the article on High Pass sharpening in last month’s issue. I’ve heard that sharpening in Lab color mode can benefit your images as well; can you explain how to perform this sharpening technique in Lab color mode?


We’re glad you liked the article “Bring out your image’s detail with High pass sharpening.” As we explained last month, using the High Pass filter is a great way to sharpen an image because it’s nondestructive to your original image. Most of the time you’ll perform your image sharpening in RGB mode, but there may come a time when you’ll want to change to Lab Color mode.



While an image in RGB mode can handle a small amount of sharpening, image quality can degrade when larger amounts are applied. This is because instead of sharpening the luminance values in the image, the sharpening is applied to the color information, which often responds by creating “color noise” such as purple fringing and chromatic aberration.



You can avoid these problems and get better results by converting the image to the Lab Color space and doing your sharpening there. Keep in mind that you can be a little more aggressive when sharpening in Lab mode, but it still has its limits.


To perform high pass sharpening in Lab color space:

1.       Open a flattened RGB file, and choose Image > Mode > Lab Color.

2.      Duplicate the Background layer, and keep the copied layer selected.

3.      Select the Lightness channel in the Channels palette so it’s the only one visible as shown in Figure A.