Sharpening using Photoshop's Unsharp mask

deemarie · December 19, 2005 9:47 am

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.
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.
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.
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
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.

  • 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

Article Comments

theoriginalphoenix ( posted at 12:00AM Thu, 22 December 2005

Im new here and an avid photographer as a hobbiest and just entering the world of digital photography so ever little tidbit of info that i learn is greatly appreciated this whole 35mm to digital is freaky but Banzai! thanks Paula im sure I`ll try it

nickcharles ( posted at 12:00AM Sat, 24 December 2005

Awesome, Paula! I just tried that out, and it does make a difference. Thanks for the info!

Aeneas ( posted at 12:00AM Sat, 24 December 2005

The main problem with this method is that the unsharp mask simply sharpens everything. In fact: there is no sharpening at all. What really happens is that the filter (and all sharpening filters) increases the difference between neighbouring pixels. One can set the minimum difference that is needed to get a "sharpening" effect, but there is no choice where exactly this will happen. So for example grain is also "sharpened". Which is why it is best to use an edge mask. An edge mask is a mask that protects everything except the edges. When you then use sharpening, only the edges are sharpened. Creating an edge mask is not that difficult: duplicate the channel with the best contrast and work on that. Take the stylize>find edges filter and invert the result. Then use Noise>Median set to some 2 to get clear edges. Now make the edges thicker with Other>Maximum set to some 4. Next step is to blur this with Gaussian Blur set to the same value as the one you used for maximum. Go back to composite view and click the mask (channel) you created. You can now use a much higher value of unsharp mask as everything is protcted, except for the edges.

firstepop ( posted at 12:00AM Sun, 25 December 2005

Great, This showed up at the right time. I was working on a small photo of an eye and was trying to enlarge it without a lot of degradation. I just tried this tutorial and it works well enough for me to get the job done. Thanks again!

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