Sharpening Techniques

Sharpening is a critical part of the digital process, yet it’s often misunderstood. Sharpening isn’t about making a blurred image sharp; it’s about getting the optimum sharpness from a photo that was shot sharp. An image direct from a sensor or a scanner isn’t at its optimum sharpness. There are a number of reasons for this because of the technologies involved. So that image has to be sharpened in order for it to look as good as the lens that created the image on the sensor or film.

There are many formulas and ideas for sharpening. They all work, but they don't all necessarily work best for every photographer. A sharpening technique perfect for a rocky landscape may be inappropriate for a foggy seascape. Sharpening is also subjective. Some photographers like stronger sharpening than do others. I’ll give you some ideas about sharpening that work, but I should warn you that you may hear some different advice than mine. That doesn’t make any of the advice wrong—it just points out how subjective this is because, most likely, all of the advice works.

I’ll review how to set up all the sharpening controls for your photographs, but first, I want to talk about one aspect of sharpening that will set apart many photographers—the use of Radius in Unsharp Mask and other sharpening tools. Sharpening affects the details where there's contrast along an edge (which is what sharpness is based on). Radius is where the sharpening occurs. Radius tells the program how far to look for this contrast and is strongly influenced by the size of the photo.

A large photo has more pixels, so theoretically, you need slightly more Radius for the same effect on a smaller photo. I generally use a Radius between 1 and 1.5 for most images, going up to 2 for a very large print (with a file size of more than 30 MB) and going to less than 1 for small prints (with a file size of 6 MB or less) or for subjects that don’t need a lot of sharpening. I vary the amount of Radius depending on the subject.

Those numbers are a bit controversial for some photographers. They represent a more aggressive use of Radius than some photographers like—there’s a danger of unsightly halos of brightness around strongly contrasted edges. To avoid those halos, many photographers set Radius at about half of what I do.

So why do I like the higher settings? The benefit is intensified tiny highlights, which give the image a stronger feeling of brilliance and snap. Brilliance is complementary to sharpening, but it’s not the same thing.

Top lenses often have a level of brilliance that gives an image snap and sparkle that lower-priced lenses can’t match, even though a given lower-priced lens may have similar resolution (sharpness). Brilliance isn’t something you necessarily want when shooting portraits (it makes the skin texture more obvious), but it really does help landscapes and other nature photography.

As Radius increases, tiny specks of bright highlights intensify—this is the halo "problem" on a small scale, but in this case, it helps the photo. This shows up in the overall image on your screen as long as you have a large enough monitor with high monitor resolution. This is also why I don’t enlarge the main image to 100 percent—you miss the brilliance effect. I’ll watch the 100-percent image preview in the Unsharp Mask box to be sure I’m not having halo problems, however.

An important caution: Note that the numbers used for Radius aren’t high. Most of the time, I use 1.5 or lower (because I’m dealing with images from sensors less than 10 MP in size).

Unsharp Mask is the basic sharpening tool to know and use. Smart Sharpen can be used in Photoshop, plus there are Photoshop plug-ins that help, which I’ll discuss in a moment. Still, Unsharp Mask (or USM, as it’s often called) is an excellent sharpening tool because of its control.

USM has three basic controls: Amount, Radius and Threshold. They work together—if you’ve seen many formulas for USM, you’ll notice that as one changes, the others change, especially Amount and Radius, as noted above. Any number for Amount, for example, is meaningless without knowing a Radius. Here are some ideas on how to set them:

• Amount is the intensity of the sharpening. It needs to be higher when detail is fine, Radius is low, and any time you need more
sharpness from a subject (again, you can’t get sharpness from a blurred photo and increasing Amount will make such a photo look ratty). You’ll generally use higher settings for highly detailed subjects, such as rocky landscapes, and lower settings for gentle subjects, such as selective-focus flowers. I like an Amount of 130 to 180 for nature subjects depending on the actual subject and based on the Radius I like
to use as described above.

• Radius is described in detail earlier in this column. But to summarize, I generally use a Radius between 1 and 1.5 for most images, going up to 2 for a very large print (with a file size of more than 30 MB) and going to less than 1 for small prints (with a file size of 6 MB or less).

• Threshold affects when the sharpening occurs based on contrast of an edge. A low Threshold gives high sharpness, but it also sharpens noise and other artifacts. A high Threshold reduces small detail sharpness. For most digital cameras, I use a Threshold of 3 to 4. If I find any noise problems, I increase this to 10 to 12, but never higher. I look for grain in scanned images to set Threshold with film, again never going above 10 to 12, but using low numbers when I can.

Smart Sharpen in Photoshop uses totally new algorithms for sharpening compared to USM. Still, its controls work similarly to USM, allowing you to set Amount and Radius, but it has better compensation for halos and other artifacts.

Unfortunately, Smart Sharpen has no Threshold setting. That’s a severe limitation to me and keeps me from using it as my main sharpening tool. Without a Threshold setting, Smart Sharpen often increases the appearance of noise in a photo, and for that reason, I use it on a restricted basis.

I like Nik Software Sharpener Pro for printing. This is a Photoshop plug-in (though it works in other programs, including Photoshop Elements). Sharpener Pro does some nicely automated sharpening for specific printer types, print sizes and viewing distances. You don’t have to know anything about USM settings because it doesn’t use them. It uses terms like Size and Viewing Distance that are more intuitive. It also uses some advanced sharpening algorithms.

But the biggest benefit comes from the Advanced settings in Sharpener Pro. There you can tell the program how much to sharpen areas based on their colors and tones. This allows you, for example, to not sharpen a color or tone that has a lot of noise (noise is most common in specific colors or tones). The program smartly finds these areas and sharpens only what and how much you tell it to sharpen. It does a nice job with tiny highlights, too, bringing out image brilliance as well.

You should sharpen a photo based on its printed size. Size has a big effect on what details show up in a photo and how the image should be sharpened. This is especially true with Radius choices, so a photo should be sized before sharpening. In addition, there are good reasons for sharpening a photo late in the image-processing workflow. Many adjustments to an image can affect detail rendition and noise, both of which affect sharpness. Sharpening too early can result in less than optimum sharpening for a subject, plus it can result in sharpening artifacts that are intensified from the work on an image.

Editor Rob Sheppard will be leading a digital workshop and tour to Costa Rica in December. For more information, see the Holbrook Travel website, www.holbrooktravel.com (click on Nature Travel).