Today’s Question: Your answer about the Masking slider for sharpening in Lightroom Classic to avoid sharpening the sky reminded me (I think) that there was a way to prevent smooth areas from being sharpened when sharpening a photo in Photoshop? Is that the case, and if so where do I find it?
Tim’s Quick Answer: Yes, the Unsharp Mask filter in Photoshop includes a Threshold slider, which enables you to prevent sharpening smooth areas of an image similar to the effect of the Masking slider for sharpening with Lightroom Classic or Camera Raw.
More Detail: Sharpening is a process of enhancing edge contrast in areas of the image that already exhibit contrast. This contrast enhancement causes contrast edges in the image to have greater contrast and to transition over a shorter distance, increasing the perceived sharpness of the image. This is a good thing in general, but it can be a problem if you are enhancing texture in areas of the image that should be smooth, such as a clear blue sky.
While the Unsharp Mask filter in Photoshop isn’t as advanced as the newer Smart Sharpen filter, it does include a Threshold control that enables you to exercise control over preventing sharpening from being applied to smooth areas.
You can find the Unsharp Mask filter on the menu at Filter > Sharpen > Unsharp Mask. The Amount slider controls the strength of the sharpening effect. The Radius slider determines how far outward from contrast edges the sharpening effect will extend. The Threshold slider allows you to specify how much contrast much exist before sharpening is applied.
The default value for Threshold is zero, meaning sharpening will be applied to the entire image, anywhere contrast exists between neighboring pixels. Increasing the value for Threshold will require more contrast before sharpening is applied.
Generally speaking, when you want to prevent sharpening from applying to smooth areas within an image, a value for Threshold of somewhere around 10 to 20 will generally be more than adequate. I prefer to apply very strong sharpening initially with exaggerated values for Amount and Radius, as I fine-tune the value for Threshold to ensure sharpening is applying only in areas where I want it applied. I’ll then reduce the values for the Amount and Radius sliders to more appropriate levels for the image.
As noted above, the newer Smart Sharpen filter is more advanced in some ways than Unsharp Mask. However, because of the Threshold slider that is available for the Unsharp Mask filter but not with Smart Sharpen, I often favor Unsharp Mask for images where I want to be able to control the sharpening effect with greater precision in order to maintain the smoothness of smooth areas of a photo.
