If we got a nickel for each time we've been asked what sharpening settings someone should use, we'd probably be sipping wine on a tropical island rather than writing books on Photoshop. Of course, we couldn't really come up with a short answer any less lame than "it depends."
The longer answer, of course, involves explaining the various factors on which it depends, which we'll now proceed to do. First, a necessary disclaimer: Bruce and his colleagues at PixelGenius publish a sharpening plug-in, called PhotoKit SHARPENER. While we'd be pleased as punch if you considered purchasing PhotoKit SHARPENER, you should know that a lot of what it does is based on the information in this chapter. The plug-in just does it a lot faster than you can do it manually.
Why We Sharpen
Wethat's a collective "we," which we hope includes you, toosharpen images for several reasons, including the inevitable loss of sharpness from the capturing process. Every reason to sharpen imposes its own demands. Fairly often, though, these demands contradict one another.
Sharpening the capture
Whenever you turn photons into pixels, you lose some sharpness, because no matter how high the resolution of your capture devices, they sample a fixed grid of pixels, turning the continuous gradations of tone and color that exist in the real world into discrete pixels. Each capture device imposes its own noise pattern on the image, whether it's from film grain, from digital noise, or, as is common in many film scans, from a combination of the two.
You need to sharpen the image content to restore what was lost in the conversion to pixels, but you don't want to also sharpenand hence emphasizethe noise and grain. So effective sharpening must take into account the source of the image.
Sharpening the image
People often sharpen for creative reasons: to tell a story, to make a point, to emphasize an area of interest, or to sell a product. To do this successfully, you need to match your sharpening to the content of the image. A busy, high-frequency image with lots of tiny details, like a forest full of trees, has much narrower edges than a close subject with soft detail like a head shot or pumpkin (see Figure 9-7).
Figure 9-7. Unsharp Mask settings for high- and low-frequency images
When sharpening image content, you want to emphasize the edges without overemphasizing textureslike skin tonesand without introducing spurious texture into flat areas like skies. So effective sharpening must take into account the image content.
Sharpening the output
When you turn pixels into marks on a substratein other words, when you printyou lose sharpness again. In most cases, individual pixels aren't translated into individual dots of ink or dye, and even in those cases where they are (such as photographic printers like the Durst Lambda or Fuji Pictrography) the printed "pixels" tend to be round rather than square. In either case, the output loses some sharpness. Because you want to make the print as sharp as the output device can render it, effective sharpening must take into account the output process.
When We Sharpen
Needless to say (but we'll say it anyway), the chances are exceedingly slim that you can satisfy all these different sharpening criteria with a single round of Unsharp Mask, applied globally to the image. Of course, if one pass of Unsharp Masking is all you have time for in your workflow, it's better than not sharpening at all. But for the highest quality, we recommend using a two- or three-stage approach to sharpening. Rather than try to satisfy all the criteria simultaneously, this workflow approach to sharpening addresses them separately.
First, apply a gentle round of sharpening very soon after image capture to take care of the source-sensitive aspects. After you make your major tone and color corrections, apply some localized creative sharpening (we skip this step in automated workflows). Then, once the image is at final output resolution, apply sharpening tailored to the chosen output.
At the risk of drawing an analogy from one incomprehensible subject to another, we liken the sharpening workflow to the color management workflow:
Essentially, the capture and creative sharpens make a file that is repurposable (our mothers always taught us to keep our options open as long as possible), and responds well to resizing and final output sharpening.
Of course, if approached carelessly, this workflow can create some very ugly images. Just hitting the image with three rounds of Unsharp Mask using different radii is a recipe for certain disaster. Instead, retaining optimum quality requires finesse and some fairly advanced sharpening techniques. We look at individual sharpening techniques in detail later in this chapter, but here's the 30,000-foot overview.
The first round of sharpening in the workflow must be done very gently indeed; otherwise the result is likely to be a hideously oversharpened mess. It's often helpful to sharpen through an edge maskso that only the high-contrast edges get sharpenedand to focus the sharpening on the midtones, protecting highlights and shadows so that they don't get driven to solid black and solid white.
With very grainy or noisy originals such as high-ISO digital capture or fast color negative, you may first want to apply some noise reduction (essentially unsharpening) using the Reduce Noise filter or a third-party noise reduction plug-in.
For creative sharpening, you can build "sharpening brushes" to paint your sharpening just where you want it. As you'll see, you do this by creating a new merged layer, setting the layer's blending mode to Luminosity (to avoid color-fringing), applying a global Unsharp Mask to the layer, then adding a layer mask set to Hide All. As you paint on the layer mask, Photoshop adds or removes the sharpening.
Creative sharpening effects are really only limited by your imagination. For example, one way to make an object appear sharper is to blur its surroundingsyou can create "smoothing brushes" using the same techniques as sharpening brushes, but substituting a blur for the sharpen.
Since the image-specific and source-specific concerns were already addressed in the capture and creative sharpening phases, output sharpening can concentrate solely on the output process.
Note that you can only sharpen the image's pixelsPhotoshop has no control over how those pixels are rendered to ink on paper (or any other output process). So the key factor in output sharpening is the relationship between the pixels and the resulting hard copy. Hence output sharpening must be done at the final size and resolution, often as the last step before converting an RGB file to CMYK and saving the file to disk. Note that unlike capture and creative sharpening, output sharpening is something we always apply globally. Here are a few other considerations:
Someday, RIPs and printers may even be able to apply output sharpening on the fly, particularly if things like color conversions and trapping are also going to occur there. But for such an approach to succeed, the device will somehow need to know the state of the incoming images (what kind of sharpening has already been performed, and so on).
The Sharpening Workflow
We'll be the first to admit that taking a workflow approach to sharpening is a fairly radical idea, but the more we use it, the more we find that it makes sense. We've done a great deal of testingBruce reckons he sharpened about 5,000 images to build and fine-tune PhotoKit SHARPENERbut plenty of work remains to be done.
The results of two- or three-pass sharpening often justify the extra pains, especially with images we plan to reuse for several different types of output. However, if you're in a hurry, and you're preparing an image for one-off reproduction (particularly with a low screen frequency that can only show a limited amount of detail anyway), one-pass sharpening may make just as much sense.
We don't claim to have solved every conceivable sharpening problem. The techniques that follow are ones that we use every day in our sharpening workflow, and as we describe them, we'll tell you how we use them. But feel free to pick and choose, and to adapt them to your own work.