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Advanced Sharpening in Adobe Photoshop

Sharpening can seem like such a simple concept. In the quest to get the best results though, the topic can start to become more and more complicated. As with everything in Photoshop, there are many ways to approach sharpening. This week we'll take a look at the brand new Smart Sharpen filter in Photoshop CS2 as well as a technique for edge masking that can improve your results with any sharpening method.

Smart Sharpening

Smart Sharpen dialogEven though Photoshop is already an extremely impressive piece of software, Adobe keeps hard at work looking for ways to make it even better. The newly released Photoshop CS2 is their latest giant step forward on that quest. I'll be starting to cover some of the new features with next week's article, but can't resist jumping in this week with some coverage of the new Smart Sharpen filter. I'm still learning about some of its advanced features myself, but from what I've seen so far, it's a real winner.

As with Unsharp Mask, Smart Sharpen makes use of a Radius and an Amount to control the degree of effect. Unlike Unsharp Mask, it has the capability of removing or diminishing various kinds of blur. For photographic images, you will probably want to select Lens Blur, but you may also want to experiment with removing Gaussian Blur and Motion Blur.

So far, I've found that a Radius between about one and five pixels is more than adequate to get good results. Larger images such as those sized for print, or those with less fine detail can utilize higher Radius values. Those sized for screen display, or those with greater amounts of fine detail will tend to work better with smaller Radius values.

After setting the Radius, be sure the image is set to a full 100% view and adjust the Amount to get the desired effect.

At the bottom of the window is the "More Accurate" checkbox. Since Smart Sharpening can be reasonably CPU intensive, you may find it preferable to leave it unchecked while adjusting the other controls. Be sure to check it before clicking "OK" though.

If you click on the Advanced radio button, you will gain a Shadow and Highlight tab that will allow you to fade the effect in certain areas. If you have an undue amount of noise in the shadow areas for example, you can fade the sharpening effect accordingly to avoid accentuating that noise.

Smart Sharpen even allows you to save collections of settings to simplify repeated use. If your settings include Advanced options, they are retrieved even if the dialog is set to Basic mode when later used.

Edge Masking

Regardless of which method you employ, you can sometimes find yourself wishing you could sharpen more but not wanting to risk causing incidental detail, noise, or grain in non-edge areas to become exaggerated. All the methods I've discussed are already designed to work mainly on edges, but if you want to be sure you aren't affecting anything else, you could always use the lasso or other selection tools to exclude everything else. This would be an incredibly tedious process though, and there is a better way.

First, select and copy your entire image to the clip board with Select >> All, followed by Edit >> Copy. The result of running the 'Find Edges' filterNow click on the Channels pallet and create a new channel using the icon at the bottom of the palette. Photoshop will automatically assign it the name "Alpha 1" (assuming you haven't created any other channels yet) and deselect all other channels. Use Edit >> Paste to fill this new channel with a grayscale version of your image. By the time we are done, this new channel will help with sharpening the image, but no one is ever going to see the channel itself.

With this new channel selected, use the Filter >> Stylize >> Find Edges filter. It doesn't have any options so it will immediately run, turning the contents of this channel into something akin to a line drawing. All the edges will show up in black, with the background white. To make the effect even more apparent, open up the Image >> Adjust >> Levels dialog. With the Preview box checked, drag the black point slider all the way over to the beginning of the histogram and move the middle (gray point) slider to the left until it is almost on top of the black point slider. To clean up the background, move the white point slider to the left a bit until you have a reasonably clean white background but haven't yet started to lighten the black edges. Adjusting Levels after running the 'Find Edges' filterMove the sliders around until the edges themselves show up as cleanly as possible against the background. Click on "OK" when you get things looking the way you want them to.

Next, look at what you have in this channel carefully. In the end, the black areas will be the ones we'll be apply sharpening to, so if there are areas that were left as black after adjusting levels, use a white paintbrush or pencil tool to paint them out. This doesn't need to be perfect, but does give you the opportunity to fine tune the areas to be sharpened.

Now, smooth the edges a bit by applying a slight blur with Filter >> Blur >> Gaussian Blur. Only a small amount is necessary, so use something in the range of two to five pixels. The intent is to avoid the possibility that the transition between what will get sharpened and what won't will show up in the final image. If you raise the amount too much, the edge lines will visibly lighten, so don't overdo it as this would diminish the whole intent of selecting just the edges.

Next, we're ready to turn out slightly softened line drawing into an actual selection. Open the Load Selection dialog by accessing Select >> Load Selection from the menu. Be sure the source is set to the "Alpha 1" channel of your document. Check the Invert checkbox to be sure we select the black parts instead of the white parts as a normal mask would. Click on "OK" to close the dialog.

Go ahead and click on the RGB channel to return your image to a color version. If you've done it right, you should now see the familiar "marching ants" outlining each edge area. To get the dotted selection lines, go to View >> Show and uncheck "Selection Edges." Your image will now look like nothing ever happened, but the edges will still be selected. We just turned off the visual queues that this is the case so we can get rid of the distraction while actually sharpening — which is the next step, by the way.

All of the above may sound like a lot of steps, but now that we have selected just the edges in our image, we can afford to be much more aggressive in sharpening without fear that anything other than edges will be affected. Go ahead and use whichever sharpening method you prefer at this point. You should find that you can do a lot more without any adverse effects. Be sure you are viewing your image at the full 100% view to be sure you don't overdo it in your excitement. Also remember that even though the selection dots aren't visible, they're still there, so use Select >> Deselect when you are done sharpening.

At this point, you can feel free to delete your "Alpha 1" channel if you want, or leave it there for possible future use. If you do want to keep it, you may want to rename it by double-clicking on its name in the Channels palette.

All together, sharpening with an edge mask can involve a fair number of steps, but when you find a technique you really like you can automate it by creating an Action.

Since Smart Sharpen is new with Photoshop CS2 and edge masking involves extensive use of Channels, I'm afraid neither can be used with Photoshop Elements.

Comparison between various sharpening methodsA Quick Comparison

The best way to get a feel for different ways to sharpen is to experiment on your own images, but as a quick comparison, I decided it might help to show a close-up sample of an image sharpened in various ways. Shown here are various versions of a 200% view showing the edge of a Nikon BR-2A reverse mount lens ring. The original unsharpened image is notably soft at this scale. Applying an unsharp mask improves things considerably, but this is about as sharp as I can make it before halos start to show at high contrast edges. The High Pass sharpening method improves the type and other edges, but the texture of the metal in reflective areas is also getting sharpened now. With Smart Sharpening I'm able to sharpen the lettering even more while avoiding the noisy appearance of the metal texture, but the final version using Smart Sharpening and Edge Masking looks even better. Keep in mind that these are 200% views yet the final version looks almost as if it could pass for a 100% actual pixel view.

As a slight point of clarification for the eagle-eyed, I have rotated these close-ups slightly to allow me to stack all five of them, one above the other, while using up the minimum amount of screen area. This edge section in the original image is at more of an angle than shown here.

Other Methods

There are a number of third-party tools that automate or augment the methods I've covered here. True to the spirit of innovation, new ones pop up all the time and existing ones come out with new versions. As I write this though, my favorite of the lot is Pixel Genius's PhotoKit Sharpener. Available for both Windows and Mac OS, it's not inexpensive (about a hundred bucks), but it is good. It works on both 8-bit and 16-bit images and takes a well thought out systematic approach to sharpening for most any need. While it employs some very clever algorithms, all the complexity is handled for you. You need only tell it your requirements and runs through the needed steps, producing results on one or more new layers so you can fine tune things using layer opacity as needed.

Nik Sharpener Pro, another popular choice just released their long awaited version 2.0 with support for 16-bit files. Produced by Nik Software (formerly Nik Multimedia), a company most famous for their Color Efex Pro filters, Sharpener Pro is even more expensive than PhotoKit (over $300 for the complete thing) and I'm not sure that I can see a rationale for buying it. They have a free download trial edition if you want to check it out for yourself though.

Finally, you'll notice I haven't mentioned the basic Sharpen, Sharpen Edges and Sharpen More filters on the Filter >> Sharpen menu and you may have been wondering why. The short answer is that they really aren't worth mentioning. Even basic Unsharp Masking will give you better results without much effort so you are better off simply ignoring these less sophisticated methods.


Date posted: May 8, 2005

 

Copyright © 2005 Bob Johnson, Earthbound Light - all rights reserved.
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Previous tip: The High Pass Way to Sharpen in Photoshop Return to archives menu Next tip: Color Management Changes in Photoshop CS2

Related articles:
Behind the Unsharp Mask: The Secret World of Sharpening
The High Pass Way to Sharpen in Photoshop
Really Smart Sharpening
Sharpening in Adobe Lightroom 3
The Best Way to Fix Over-Sharpening
 

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