To minimize the accentuation of noise, Luminance sharpening requires that the Unsharp Mask’s Threshold value be set precisely. When this isn’t enough, Edge sharpening adds a mask that targets the contours of an image, allowing more aggressive sharpening with fewer side effects. Like Edge sharpening, High Pass sharpening (named for the filter used to produce the effect) targets contours in an image, but it does so without the need for a mask. Unlike Edge sharpening, the contour accentuation it produces is soft, feathered and wide. The effect is substantially different and can be used for many creative effects. High Pass sharpening is very similar to the effects of ACR and Lightroom’s Clarity slider, but it offers more control and more varied effects.
Follow these steps to apply High Pass sharpening:
1. Duplicate the layer that’s to be sharpened.
2. Change the mode of the duplicate layer to Overlay. This is what generates the contrast effect.
3. Filter the duplicate layer and apply the High Pass filter (Filter > Other > High Pass) using a Radius setting that accentuates edge contrast without producing halos. This gives the image layer a gray and linear appearance, concentrating the contrast on contours.
4. Desaturate the filtered layer. Higher Radius settings leave more residual color, and you can get considerable saturation shifts.
5. Double-click the layer and use the Blend If sliders to remove the effect from near black and/or near white values. Start by moving the This Layer highlight slider to 235, holding the Option/Alt key and splitting the left side of the slider to 215; finish by moving the This Layer shadow slider to 25, and holding the Option/Alt key, split the right half of the slider to 45.
6. Optionally, reduce the layer’s opacity and/or mask it as desired.
High Pass sharpening usually does not require a mask, but masking a High Pass layer can provide sophisticated local control, such as reducing the effect with a gradient mask, which is particularly useful for hybrid sharpening.