In photography, one of the most satisfying sensations is bringing an object into focus. If you’ve ever used a manual-focus camera, you know the pleasure of gently twisting the focus ring until your subject is perfectly clear.

But even autofocus fans can achieve similar satisfaction using Photoshop’s Sharpen filters. The program has several. This month we’ll explain the differences among them and show you how to use them.

Get the point? Just because a camera has an autofocus feature doesn’t mean its images won’t need sharpening. Various conditions can reduce the clarity of an image. Low light, a moving subject, or an unsteady photographer’s hand can all blur an image. If your subject is slightly out of the foreground, this too can cause poor focus. Or, if you are scanning paper prints, a poor scan can cause blurriness.

To begin. Create a new folder on your Desktop called Sharpen. Copy a few of your favorite photos here for practice. (This way you don’t have to worry about damaging originals.) The photos can be JPEG (Joint Photographic Experts Group) or TIFF (Tagged Image File Format) files. If you don’t have any practice images, copy one or two of Photoshop’s sample images to your Sharpen folder. Locate the sample photos in C:\PROGRAM FILES\ADOBE\PHOTOSHOP 6.0\SAMPLES.

Honing The Blade

Open a photo. Go to the Filter menu and select Sharpen. You’ll see four options: Sharpen, Sharpen Edges, Sharpen More, and Unsharp Mask.

The Sharpen tool works by increasing the contrast of adjacent pixels. Sharpen More is equivalent to using the Sharpen tool several times. The Sharpen Edges tool is a little smarter: It only sharpens where it detects an edge, which is defined as a large shift in brightness. It leaves more homogonously bright areas untouched.

Practice with these three tools. Oversharpen an image. You will see how pixels get so distorted that they actually introduce a new type of blur, a colorful noise, which is caused by rendering pixels too bright. In photos featuring people, sure signs of oversharpening include bright spots on eyes, glasses, or teeth. To undo your work, go to Edit, Undo or Edit, Step Backward. (If you’ve really changed things, go to File, Revert. This will take you back to your last saved version of the image.)

Unsharp Mask

The seemingly oddly named Unsharp Mask filter gives you the most control over the sharpening task. (Unsharp masking is actually a traditional film technique intended to sharpen edges.) In Photoshop, this filter lets you specify a threshold for determining differences between adjacent pixels, which increases or decreases contrast. And it lets you increase or decrease the radius of the sampling area around edge pixels. If your goal is to create a printable image, keep in mind that the effects of the Unsharp Mask are more pronounced for on-screen vs. printed images. In other words, print samples before deciding on your sharpness settings.

Adjust sharpness. Here’s how it works. Open an image and select Filter, Sharpen, Unsharp Mask. You’ll get a dialog box; click the preview box. (This way the changes you make appear across the entire image, not just in the tiny sample window.)

The first slider determines the amount of sharpening. For a high-resolution printable image, a standard level of sharpness is 150% to 200%.

Radius. The Radius slider determines the number of pixels surrounding the high-contrast edge pixels the sharpening will affect. The higher the number, the wider the band of pixels affected. A lower number ensures that only edge pixels will be sharpened. For many images, a radius between 1 and 2 is good.

Threshold. The Threshold slider determines how different adjacent pixels must be before they are considered edge pixels and therefore sharpened. The higher the Threshold value, the greater the contrast there must be between pixels. A Threshold value of 0 (the default) sharpens all the pixels in the image. Depending on the image, values between 2 and 30 work well.

To better visualize how these tools affect edge pixels, boost the magnification of the sample window to 300%. Use the hand tool and move to a high-contrast edge. Increase the radius to 3 or 4 to see how the edge widens. Increase the threshold to see how the edge thins.

To get a feel for the Unsharp Mask tool, set the Radius to 2 and the Threshold to 20. Then play with the sharpen slider. Remember that printed results will look different from those on-screen. When you’re satisfied, save your work.

The difference between a sharp and a blurry image can be dramatic. Doesn’t it feel good to sharpen your focus?