Why is a filter that makes images appear sharper called Unsharp Mask? In silver-halide-based photography, unsharp masks are made with out-of-focus negatives that are registered with an original positive image. During exposure, the blurring adds contrast around contours, making images appear sharper. Digital unsharp mask works the same way; it uses blurring algorithms to add contrast to contours, again making images appear sharper.
What are the ideal settings for Photoshop’s Unsharp Mask filter? There are no ideal settings that will accommodate all images—or image makers. Settings will be influenced by resolution, ISO, subject and practitioner. As creative sharpening is primarily an aesthetic decision, individuals are likely to prefer different amounts and types of image sharpness. When it comes to the effects Unsharp Mask generates, there’s a general range of believability most viewers share, but whether you play it safe or push the envelope is entirely up to you. You can craft your own sharpening style. To do this, you have to know how the tool works and what to look for.
What are the controls Unsharp Mask offers? Unsharp Mask offers only three controls: Amount, Radius and Threshold. What do they do? Amount controls contrast; a higher setting will create a brighter halo, darker line and contrastier texture. Radius controls how thick halos and lines get. Threshold suppresses the effect in adjacent pixels, based on their relative luminosity; with a very low setting, only adjacent pixels that are very close in color will be affected; with a very high setting, many more color values will be affected.
It’s one thing to hear this. It’s another to see it. To test the filter for yourself, take these six easy steps.
1. Apply the filter to an image containing a range of textures; set all three sliders to their lowest settings.
2. Raise the Amount all the way to 500%. Nothing will happen because it’s not the effect; it modifies the effect.
3. Raise the Threshold all the way to 255; then return it to 0. Nothing will happen because it’s not the effect; it modifies the effect.
4. Raise Radius. You’ll see a dramatic change in your image. What will you see? Bright lines (halos) and dark lines (lines) will appear and grow thicker. Texture will increase. Contrast will increase, particularly around contours and with respect to texture, which may make luminance noise more pronounced. Saturation will increase; color noise may begin to appear.