Sharpening in Adobe Lightroom 3
I've written a number of articles on how best to sharpen images in Adobe Photoshop but Lightroom can do an outstanding job of sharpening as well. If you're used to sharpening in Photoshop, the technique is similar in Lightroom, but much better. Here's the basic rundown.
First, as with all things in Lightroom, sharpening is processed non-destructively. It never actually changes the underlying pixels of your image. Everything it does exists solely as a list of instructions to be applied on-the-fly to your image preview. These instructions are stored along with all your other adjustments when you save your image. When you open it next time, everything is right where you left it. All your adjustments look like they are part of your image, but the really aren't. If you subsequently make more changes, nothing has been lost or degraded as a result of your earlier choices. You can tweak things as much as you want until you are satisfied, with no more loss than if you had made those same choices in the beginning. None of those edits actually get baked into your image until you print it or export it from Lightroom.
It's also worth pointing out that sharpening in Lightroom only ever affects the luminance channel of the image, not the color. As such, problems of fringing and color shifts are far less likely than when working in RGB mode in Photoshop.
Before you start sharpening, open your image in the Develop module and create a virtual copy by right clicking on the image in the main window and selecting "create virtual copy." This will let you use View >> "Before / After" to easily see the net effect of your sharpening. Making a virtual copy isn't required, but it can be helpful and there's little reason not to. Lightroom virtual copies don't take any real space since they exist just as a second set of adjustment instructions rather than a second copy of the image pixels themselves. Remember, Lightroom never changes your actual image pixels.
The controls for Sharpening in Lightroom are located in the Detail panel of the Develop module. The interface looks straightforward enough. At the top of the section is a small detail zoom preview window. Underneath that you'll find four sliders. But before you just start pushing those sliders around, let's take a look at what each of these does.
By default, the zoom preview shows you a 1:1 view but the scale can be changed in much the same way as the main image view window. If you click on it with your left mouse button, the zoom will toggle between this close-up view and an overall view of your image. Click again and it goes back to the zoom view. If instead you right mouse click the zoom preview you can change to close-up to be a full 2:1 view. This larger-than-life view can lead to a mistaken impression of what your image looks like unless you are careful so I'd suggest leaving the zoom preview at the standard 1:1 view for most situations.
What I generally do is to set the zoom preview to 1:1 and adjust the main Develop view panel to 1:2. The fifty-percent view, or 1:2, works well to gauge the degree of sharpening and the 1:1 zoom preview helps check detail areas when needed. With this configuration, checking the overall view of the image requires just a single mouse click on the main image to toggle it to the "fit" view so you can see the whole thing. Click again and I'm back to the 1:2 view.
To move the zoom window around the image, either click on it and drag, or click on the small cross-hairs icon to the upper left of the zoom preview and then move your cursor over the main image. As you do, the zoom preview will track your mouse movements. Clicking on the main image will end the tracking and lock the zoom preview where you clicked.
There's also a down-arrow icon to the upper right of the zoom preview that will let you collapse the Detail panel to get rid of the zoom preview, although I honestly don't know why you would want to do that.
Now on to the sliders.
As befits its position as the topmost slider in the Sharpening dialog, the Amount slider controls the overall amount of sharpening to be applied and is likely the one that will have the greatest affect on the appearance of the image you are working on. The farther to the right you position it the more affect it will have. If the Amount slider is left at its default value of zero, none of the other sliders can be used and will appear grayed out. You can take this as a clue that you are intended to use the Amount slider first when sharpening.
If you hold down the Alt key (Option key on Mac OS) as you move the Amount slider you can temporarily view your image purely as grayscale. In full color, your eye can easily be fooled into thinking your image is sharper than it is if the subject has a strong color contrast compared to the background. Sharpening works by adjusting contrast along edges and working in grayscale makes it easier to accurately gauge contrast. Don't worry — as soon as you release the Alt key the color will return.
The Radius slider determines how close to detected edges detail needs to be to be included in the sharpening affect. It also helps determine just where those edges are. As you move the slider further to the right Lightroom will find ever more details in your image that qualify as edges.
Just as with the Amount slider, you can hold down the Alt (Option) key while adjust the Radius slider to gain insight into how your changes will affect the image. When you do, the image will turn to a grayscale version but this time the view will be based just on the edges that Lightroom finds. Where no edges are detected the image will appear as featureless medium-toned gray. Edges will stand out as increased contrast areas in that field of gray. The view will be familiar if you have ever made use of the high-pass sharpening technique in Photoshop. Generally, you should move the slider until only major edges start to appear in the zoom preview but this will vary somewhat based on what sort of detail you want to emphasize. Remember, all your adjustments here are lossless so you can feel comfortable playing with the sliders to optimize your results for the particular image you are working on.
The Detail slider functions similarly to the Radius slider but looks only at fine detail rather than at all edges. You can safely set the Detail slider to a higher value if the Radius slider is set lower, and vice versa. The two work hand in hand. If both are set too high, watch out. If you want to accentuate only major edges, set the Radius high and the Detail low. If you are working on an image with fine detail that you want to see clearly, set the Radius more moderately and raise the Detail slider. Holding down the Alt (Option) key works the same way for the Detail slider as it does for Amount.
The Masking slider is a welcome addition to Lightroom that makes it easy to limit your sharpening to edges and keep areas that don't need sharpening unchanged. There's nothing more frustrating than sharpening digital noise that may happen to exist in what is supposed to be a clear blue sky. Masking lets you avoid this. If you are familiar with edge sharpening techniques in Photoshop, you probably already understand the intent of the Masking slider. As you move the slider to the right, only areas that truly should be considered edges will be affected with everything else masked out. If you hold down the Alt (Option) key while adjusting Masking you can see the traditional grayscale display of the mask. Areas that are black will be blocked completely from the affects of sharpening. Areas that aren't will be affected proportionally to how bright they appear in the mask display. With the slider all the way down at zero, the sharpening will be applied equally across the image. With it moved all the way up to 100 only the most obvious of edges will qualify. With the Mask slider set appropriately for an image you can more safely boost the values of the other sliders without fear of halos and other artifacts.
I really like the way Lightroom implements sharpening. Sharpening has long been problematic in Photoshop due both from a lack of good tools as well as the fact that the process is inherently destructive in Photoshop since it requires actual pixels to be modified. And since it works only on the luminance channel it is generally much easier to sharpen in Lightroom than in Photoshop without fear of ending up with something that ends up looking like you sharpened it.