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Wednesday, August 1, 2007

Sharpening Techniques

A strong use of Radius in Unsharp Mask may help your nature images

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.

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