We all know that proper image sharpening is important to maximize your image quality. The problem is that most sharpening tools are poorly explained, or we rely on “gospel truths” passed through the Internet and take settings as absolutes. The reality is that there is no “one size fits all” setting for sharpening.
The Trouble with Traditional Sharpening Techniques
There are two primary tools that we use for sharpening images: Unsharp Mask (USM) and High-Pass/Overlay filter. Both have pros and cons, but both of these tools perform essentially the same function; they enhance local contrast at edges in your images. You can change the settings in these tools to emphasize either small details (small radius settings) or large shapes and forms (large radius settings). The problem is, that many of our images have both fine details and medium to large forms. One size does not fit all.
An even bigger issue is how to deal with sharpening artifacts (halos) at high-contrast edges. The USM tool, for example, creates its effect most strongly at high-contrast edges– the places in the image that really don’t require much sharpening! With traditional (global) techniques, we’re forced to make compromises– either dial back the sharpening to prevent the halos at the expense of sharpening details elsewhere, or live with sharpening artifacts that can detract from the overall image quality.
Selective Sharpening to the Rescue
If you use an editing tool that offers local editing options (brushes, Control Points, etc.), then you can perform sharpening only to the areas that require it. That means you can use very strong USM settings in places where you won’t see artifacts, and remove the effect from areas that would otherwise show exaggerated halos.
The easiest way to perform selective sharpening, in my opinion, is via Control Points– using either Nikon’s Capture NX2 or the Nik Sharpener Pro 3 plug-in. Control Points let you make fast, accurate masks to dial back the intensity of the sharpening effect only where you need to. If you are a Capture NX 2 user, you’ll find a full explanation of selective sharpening in my training video, Sharpening Techniques for Capture NX2.
Here’s a 100% view of a high-contrast edge with global sharpening applied via USM:
While the rocks look sharp, you’ll notice the obvious sharpening halos at the boundary between rock and sky.
Here’s the same edge with selective sharpening applied via Control Points in Capture NX 2:
Notice how the sharpening in the rocks is preserved, but the halo at the sky/rock boundary is significantly reduced. That’ the power of selective sharpening!
Learn more about sharpening, including techniques for High Pass sharpening and Print/Output Sharpening, in Sharpening Techniques for Capture NX2, available for download from the Luminescence of Nature Press online shop.