How do I sharpen a digital/scanned photo?

Most scanners and some digital cameras create a slightly fuzzy image. Sharpening an image will increase the contrast at the edges. It will look more like a photographic print. Unsharp Mask can help achieve this. Sharpening too much can cause a halo effect in the image. It is better to err on the side of caution and sharpen conservatively than to over sharpen. Only run Unsharp Mask after all your other adjustments have been made.

A good explanation of Unsharp Mask can be found in Real World Scanning and Halftones by David Blatner, Glenn Fleishman and Steve Roth.

Unsharp Mask
Go to the Filter menu, select Sharpen, then Unsharp Mask. In the Unsharp Mask dialog box, adjust the Radius, Amount and Threshold.

Amount
Amount is described in Real World Scanning and Haltones as the volume setting. It controls the amount of the tonal difference between adjacent samples. This number can be played around with a bit; larger percentages produce stronger sharpening. Start with 50, but don't go over 200. Remember, be conservative.

Radius
Radius is how far out from each side of the edge the image is being affected. A large number, a lot of sample points; a small number, fewer points. A good rule of thumb is to divide the resolution of the image by 200 and use that number. So, 300 (your image resolution) divided by 200 is 1.5. Try 1 to 1.5. Remember, conservative — too high a value will ruin the image.

Threshold
This number controls how far apart the tonal values have to be before the filter affects them. Lower numbers are better. Try 1; Real World Scanning and Haltones suggests 3 to 4. Do not go above 10.

Save your file frequently as you work.

Back