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Sharpening using Photoshop's Unsharp mask

Dec 04, 2005 at 12:00 am by deemarie

I used this a lot before I started using Photoshop CS2. However, I am still so comfortable with it that I even use it with Photoshop CS2, although Adobe has added new sharpening options to Photoshop CS2. I mainly use this when I want to sharpen an image, if I resample up and increase its size. However, I only use it for small changes, not massive ones. For those I use Genuine Fractals 4 Print Pro. This process is used to prevent haloing of pixels, which can happen when you work in a color channel. It uses the Lab mode color space in the lightness channel. When I change the size of an image, often there is a degradation in quality. I have found a few ways to minimize this effect. Step One I enlarge in small increments. Let's say I had a web image that was 800 x 600 pixels at 72 dpi and I wanted to print a small version at 300 dpi. The first thing I would do to get an order of magnitude is uncheck the Resample Image button, and type in 300.
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Since many of us think linearly, in the U. S. in inches, we now know that our starting image, in its now changed state, is 2.6" x 2". Step Two Go into Image>Mode>Lab. Your color space is now Lab color.
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Step Three Start by resampling the picture using Bicubic as your choice since you will sharpen later. Possibly change the 2" height to 3". Step Four Now go into channels in your layer menu and click on the lightness channel. You will sharpen looking at an image that is not in color. Go to Filters>Sharpen>Unsharp Mask.
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Step Five Repeat these steps until you are satisfied. Also, sharpen conservatively. You might consider the amount from 50-100% per step; the radius from 1 to 2, and the threshold depending on the subject. Photoshop Help has a good discussion on the Unsharp Mask
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Step Six When you are finished, click on the top of the channels, where it says Lab (in color) and go back to Image>Mode>RGB. Working in the lightness level, helps prevent any haloing of colors.
  • I hope you can put this mini-tutorial to good use in creating your holiday images.
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  • The Paula Sander's Report is a regular Renderosity Front Page featured column, where Paula investigates and comments on graphic software, techniques, and other relevant material through her reviews, tutorials, and general articles.
December 20, 2005
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