A lesser known photo sharpening method can reveal subtle detail

How do you sharpen your digital photos? Using the camera's sharpening settings for a jpg shot is the simplest solution, but only suitable for small snapshots. If you're exploring sharpening techniques for your RAW format shots you will discover that sharpening usually takes place at multiple stages. In the RAW converter the aim of sharpening is to minimally restore critical focus of the camera's capture (not to be confused with making up for poor focus). Next, after the RAW conversion, the sharpening goal is often to enhance detail during any final color correction and photo manipulation. This may either be a global adjustment to the entire image or on selected areas like the eyes in a portrait. Sharpening at this stage is often overlooked. When it's time to print or after resizing for the web we apply any final output sharpening. It's that middle stage that we'll explore today.
Click on the luna moth photo to see it larger. Additional USM was applied after scaling.

The latest RAW converters can eliminate some of the mid-stage sharpening for many shots with their tools to enhance micro contrast. When you need to enhance the detail in subtler transitions and textures, like the blades of grass on a golf green or the furry back of a moth without over sharpening the entire photo, try the High Pass filter technique. I used it back in the 90's to bring out detail in drum scans. It's a perfect process for recovering fine detail in today's high resolution digital photos.

Photoshop's High Pass filter doesn't produce anything attractive on its own. It's designed to be used with certain layer blend modes like Overlay, Soft Light and similar modes that alter the image based on the luminosity of the layer. A 50% gray value has no effect on the layers below in Overlay mode. The further from 50%, lighter or darker, the greater the layer changes the image below. Let's see how High Pass is used.

The High Pass filter technique is simple. In Photoshop you make a copy of the RAW converted photo on a new layer. I'd suggest only using enough sharpening in the RAW converter to restore focus and staying in 16-bit. Go to the Filter pull-down menu, to Other, to High Pass. There's only one slider. Try a low setting of 2 as a test and click ok. Don't panic. The result will look very ugly. Next we want to remove any remaining color in that layer to protect the color of the photo. Simply use the Hue and Saturation tool on this gray layer, dragging the saturation slider to the left. Now the fun part. Change the blend mode of that filtered layer to Overlay and move the opacity slider. Watch the detail increase in subtle areas as the opacity increases. Too much and things look unnatural. You can use a layer mask to target certain areas of the photo with this sharpening.

Before and after - the high pass technique shows greater clarity in the hairs. 
 

High Pass sharpening is not for every shot and not a substitute for final output sharpening. Experiment and you will find the settings that work best with your workflow and camera. -pw