Trade Tricks: Sharpening The Right Way

Sharpening is an important step in the image-editing process. While it won’t make an out-of-focus image (or an image blurred by camera or subject motion) sharp, sharpening will increase the contrast between light and dark pixels at edges in the image, which makes the image appear sharper. Digital imaging provides lots of useful tools, but you still have to focus accurately and hold the camera steady when shooting.

The longtime favorite sharpening tool is Unsharp Mask because it’s simple and provides a good degree of control. In Photoshop, it’s found in the Filter menu (Filter > Sharpen > Unsharp Mask). The Unsharp Mask dialog box provides three sliders, which allow you to adjust the effect. The top slider is Amount (which controls the intensity of sharpening) and ranges from 1% to 500%. The middle slider is Radius (which controls the width of the edge sharpening) and ranges from 0.1 to 250 pixels. The bottom slider is Threshold (which controls how different pixels must be from one another to be sharpened; higher settings reduce sharpening, but also noise) and ranges from 0 to 255 levels.

Each image requires a different degree of sharpening, but here are some starting points: for a portrait—Amount 100, Radius 1.0, Threshold 6; for architecture or landscapes—Amount 150, Radius 1.5, Threshold 3; for a high-ISO image—Amount 150, Radius 1.0, Threshold 10. Compact digital cameras apply a lot of sharpening to JPEG images, so might require a Threshold setting in the 10 to 12 range. Larger image files (higher-megapixel counts) can take higher radius settings than smaller files, but generally, under 2 works best.

There are many “recipes,” and they all work as long as you don’t oversharpen. How do you know when you’ve oversharpened? If you see halos in the image, a “fish-scale” or “chattery” appearance, loss of tonal range or if the image looks too harsh, you’ve oversharpened. Reduce Radius or Amount or increase Threshold.