Advanced sharpening techniques
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Remember at this point the settings you have selected are being viewed on a monitor as a preview of the actual print. To complete the process it is important to print the image and then decide whether the image could stand additional sharpening or whether the amount used was excessive. If the settings are excessive you can choose to lower the opacity of the 'High Pass' layer. You can alternatively switch the blend mode of the 'High Pass' layer to 'Soft Light' to reduce the sharpness or 'Hard Light' to increase the sharpness.
Detail from a portrait captured on a Nikon D1x. The RAW image was processed with 15% sharpening. First test has no subsequent sharpening. Second test uses a High Pass layer (3 pixel radius) in Soft Light mode. Third test has had the blend mode of the High Pass layer changed to Overlay mode. Fourth test has sharpening via a localized Unsharp Mask (100%) in Luminosity mode. The opacity slider could be used to fine-tune the preferred sharpening routine.
Saturation and sharpening
Most techniques to increase the contrast of an image will also have a knock-on effect of increasing color saturation. As the High Pass and Unsharp Mask filters both increase local contrast there is an extended technique if this increased color saturation becomes problematic. You may not notice this in general image editing but if you become aware of color fringing after applying the High Pass technique you should consider the following technique to limit its effects.
Be aware of color fringing after you apply the High Pass technique.
Technique two: Unsharp mask/Smart Sharpen
The second technique is a continuation of the first technique and is intended to address the issues of increased saturation leading to the effect of color fringing. If a merged layer is used as the sharpening layer and this layer is then changed to Luminosity blend mode the effects of saturation are removed from the contrast equation. This second technique looks how the benefits of localized sharpening and Luminosity sharpening can be combined.
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Change the Blend mode of the High Pass layer back to Normal mode. Then apply a Threshold adjustment to the High Pass layer. Go to Image > Adjustments > Threshold.
Choose Normal from the blend modes menu in the Layers palette.
Choose Image > Adjustments > Threshold to apply a Threshold adjustment to the layer.
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Drag the slider just below the histogram to isolate the edges that require sharpening. The aim of moving these sliders is to render all of those areas you do not want to sharpen white. Select 'OK' when you are done. Paint out any areas that were not rendered white by the Threshold adjustment that you do not what to be sharpened, e.g. in the portrait used in this example any pixels remaining in the skin away from the eyes mouth and nose were painted over using the paintbrush tool with white selected as the foreground color.
Drag the histogram slider to isolate the edges that require sharpening.
