The individual photosites or "pixels" on your sensor aren’t completely isolated. To put it simply, they spill information between and among them, which reduces the sharpness from your lens.
If you shoot JPEG, you can have your camera add sharpening to the image while it’s being processed in the camera. Almost all cameras add some sharpening to a JPEG file by default, though you can turn this off or adjust it to a different level in most camera menus.
RAW files have no sharpening applied to the image file at all. You need to apply some sharpening to the image either after you’ve processed the photo in your image- processing software or during RAW conversion. Here are four possibilities.
Unsharp Mask or USM (in the Filter Menu in Photoshop or the Enhance Menu in Photoshop Elements) has been a standard part of sharpening since Photoshop started. It needs to be applied to a flattened image as a last step, after all other processing is done. The reason? There are some adjustments that you make in these programs that can cause problems if the image has already been sharpened. Plus, an image should be sharpened at its final size.
USM has three parts: Amount (the intensity of the sharpening); Radius (the distance sharpening occurs around a pixel); and Threshold (when sharpening starts to occur when two points are different in brightness). There are many formulas for these, and frankly, they mostly all work because different subjects need different amounts of sharpening. I find these numbers work well for me: Amount—100-180 (depending on the subject); Radius—1-1.5 (larger images typically need the higher amount, but watch for unwanted rings or halos around contrasty objects); and Threshold—3-6 mostly, with a maximum of 10-12 (mainly used to avoid sharpening noise).
Smart Sharpen (in the Filter Menu in Photoshop) and Adjust Sharpness (in the Enhance Menu in Photoshop Elements) are the same sharpening function, just with different names—a fairly recent addition to Photoshop products. You still need to sharpen a flattened image last in your workflow. This is a very good way to sharpen your photos, and its algorithms work well. You have two main controls: Amount (intensity) and Radius (distance).
I find that Amount looks good usually between 90 and 150, while I typically use Radius near 1 to 1.2. Choose Gaussian Blur for what you’re "removing" (I’ve never found the other options to work that well), and check More Accurate (Smart Sharpen) or More Refined (Adjust Sharpness). If you have a lot of noise in your photo, this sharpening function will make it more obvious, so you may have to use USM sharpening. There’s no Threshold setting here to deal with noise.
LIGHTROOM AND CAMERA RAW SHARPENING
If you’re using Photoshop Lightroom or Adobe Camera Raw in Photoshop or Photoshop Elements, use the superb sharpening function there. It’s superior to those inside Photoshop or Photoshop Elements. It uses totally different algorithms, plus offers some unique features. You can add this sharpening at any time—the program only will apply it at the optimum time when an image is exported or converted.
If you hold down the Alt (PC) or Option (Mac) key as you adjust any of the sliders, the sharpening appears in black-and-white, which is much easier to see. Amount is intensity of sharpening, Radius is distance, and Detail brings out detail. Lots of formulas work here, too. I find these settings useful: 40-60 for Amount; 1-1.3 for Radius; and 35-50 for Detail.
Masking allows you to block sharpening where it’s not needed. Hold down the Alt or Option key as you move the slider to the right. Wherever the screen turns black, the sharpening is masked or blocked. This can avoid sharpening noise in certain areas. Some photographers use this so that only edges are sharpened.
Nik Software Sharpener Pro offers sharpening similar to that included with Lightroom and Camera Raw, and in an easy-to-use interface that allows you to make choices such as the resolution of your printer and the paper type, plus you can selectively sharpen parts of the image.
Whatever sharpening you use, be careful you don’t overdo it. Too much sharpening makes images look harsh, gives edges strange looks and increases noise. If the photo doesn’t have sharpness from when it was shot, oversharpening isn’t going to make it sharp.