Sharpening versus Midtone Contrast — Ask Tim Grey
Today’s Question: I was always taught that the High Pass filter was a superior method of sharpening in Photoshop. And although I was aware of it, I didn’t use it much. I only learned recently that with a very small radius and use of the Hard Light mode, I can produce significant, but not overly obvious, sharpening of images with a bit of blur. What are your thoughts about High Pass? And is there a way to achieve any of these kinds of effective sharpening in Lightroom?
Tim’s Quick Answer: The “High Pass” technique is similar in overall effect to sharpening, depending on the settings used. In general practice it tends to provide more of a midtone contrast enhancement for accentuating detail, rather than a true sharpening effect. Lightroom provides similar options with Clarity and Dehaze.
More Detail: Sharpening involves (in a very general way) enhancing contrast where contrast already exists. In the context of a typical motivation for sharpening, that involves enhancing the contrast for fine details in an image in order to improve the perceived sharpness of the image.
Of course, it is also possible to “expand” that sharpening effect across a larger area so that instead of sharpening fine detail you are enhancing overall midtone contrast, reducing the appearance of haze, and adding impact to the photo in the process. This is really just a variation on a theme when it comes to sharpening.
Because there are different motivations for applying a sharpening effect (among other reasons), there are seemingly countless approaches you can take to improve perceived sharpness, increase the appearance of detail, and reduce the appearance of haze in an image. The “High Pass” technique is one of those.
The High Pass approach to sharpening (or detail enhancement) involves duplicating the Background image layer, changing the blend mode for the duplicate layer to one of the “contrast” options (such as Overlay or Hard Light), and then applying the High Pass filter to that duplicate layer (with a Radius value of somewhere around 10 pixels, though the optimal setting can vary significantly).
This approach can be very beneficial for enhancing overall detail with minimal risk of problematic halos in the image. As such, it is a technique I highly recommend. I would simply add that it isn’t really an alternative to sharpening in most cases, but rather something of a creative effect.
As for Lightroom (or Adobe Camera Raw), you can achieve a very similar effect to the High Pass sharpening technique by using a positive value for the Clarity adjustment, or for the Dehaze adjustment. The Dehaze adjustment is primarily focused on reducing the appearance of haze in a photo, while the Clarity adjustment is more focused on overall midtone contrast and enhancement of texture and detail.