Today’s Question: Can you explain the Masking slider for sharpening in Lightroom Classic? The other sharpening adjustments are familiar from similar options in Photoshop, but I can’t figure out Masking.
Tim’s Quick Answer: The Masking slider enables you to prevent smooth areas of the image from having any sharpening applied. A higher value will increase the degree to which areas with relatively low edge contrast will be protected from being sharpened. Note that this same control is available in Camera Raw for Photoshop users, in addition to being available in Lightroom Classic.
More Detail: Applying sharpening to an image enhances contrast along existing contrast edges in a photo. In other words, contrast is enhanced for the detail within a photo. For areas of a photo that have relatively smooth texture, such as the sky, sharpening can be problematic. The enhancement of the very subtle texture in these areas can create the appearance of noise or grain, which can be problematic. The Masking slider enables you to prevent smooth areas from being sharpened.
One of the great ways to get a better sense of which areas of the image will be sharpened based on the Masking slider is to hold the Alt key on Windows or the Option key on Macintosh while adjusting the slider value. This will provide a black-and-white preview of the image, where white represents areas being sharpened and black represents areas not being sharpened.
So, for example, you might increase the value for Masking until the sky area is entirely black, with the foreground being all (or mostly) white. This would cause the sky to not be sharpened, while the rest of the image still has sharpening applied.
You can refine the setting for Masking based on your priorities in terms of applying sharpening areas of the image where detail is important versus mitigating that sharpening for areas of the image with smooth textures.