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.
If trace noise and residual texture is retained in the High Pass layer, accentuating it in the image, this can be reduced somewhat without compromising the edge effects by blurring the layer or using a noise-reduction filter. Reduce these effects on the High Pass rather than on the Background layer or on a new noise-reduction layer.
You can increase the intensity of the effect by adding contrast to the High Pass layer. Use a Curve adjustment, lock down the midpoint (128/128/128), and add the amount and kind of contrast you desire.
You can accentuate the effects of the High Pass filter by sharpening the image layer with Unsharp Mask before filtering it with High Pass. Doing this will give the High Pass filter more to grab onto. Try a double pass of Unsharp Mask. First, apply Unsharp Mask with a high Radius (1.5) and a low Amount (100%); second, apply Unsharp Mask with a high Amount (350%) and a low Radius (0.5). Your settings may vary, so use these numbers as starting points to produce a maximum effect with minimal artifacts.
When you use high Radius settings for the High Pass filter, High Pass sharpening moves beyond sharpening and becomes tonal enhancement. The halos/lines it produces become so broad and feathered that they accentuate planar contrast rather than contour contrast. They also can cause localized vignetting effects, for better or worse. This isn’t surprising; all sharpening is a type of localized tonal enhancement targeted to detail (contour and texture) instead of the broader tonal scale.
It’s useful to distinguish between the qualities of High Pass contrast and Curves contrast; High Pass accentuates contours and planes first, and it produces localized effects that enhance detail and spatial relationships (objects will look sharper and more three-dimensional). Curves accentuates all tonal values equally and provides more control over the relative relationships between lights and darks, producing a smoother, more uniform effect. Your entire image will appear contrastier and more energetic. Understanding the qualitative differences between these three types of contrast—Curves, low High Pass or high High Pass—will help you decide which method to choose. You even can decide to combine them all to get even greater control over the look and feel of detail in your images. Your decision should be based not on a formula, but on the results you want to achieve with your images.
Precise sharpening can improve almost any image. Master sharpening, and you can gain unprecedented control of detail in your images and take them to a new level. Choose the type of sharpening that produces the effect that’s most appropriate for an image or that you find most pleasing. With careful consideration and consistent application, you even can create your own sharpening style and give your images a special look, one that renders your unique visual voice more clearly.
John Paul Caponigro, author of Adobe Photoshop Master Class and the DVD series R/Evolution, is an internationally renowned fine artist, a lecturer and workshop leader. Join over 20,000 other Insights enews members and get access to hundreds of digital imaging resources at www.johnpaulcaponigro.com.