What is image sharpening?

Sharpening makes a photo look crisper by raising the contrast along edges: the dark side of an edge gets a little darker and the light side a little lighter. It can't bring back detail the camera never captured, but it brings out the detail that's there. That helps photos that came out slightly soft, pictures that were shrunk for the web, and images headed for print.

Tool description

The tool uses an unsharp mask, the classic sharpening method of photo editors. Amount sets the strength, Radius the width of the edges it works on, and Threshold leaves faint detail such as noise or smooth skin alone. The preview updates live, the comparison slider shows exactly what changed, and the download keeps the image's full size.

Features

  • Unsharp mask with amount, radius, and threshold
  • Sharpens brightness only, so edges get no color fringes
  • Before and after comparison
  • Runs in your browser, so the photo never leaves your device

How it works

The tool blurs the image's brightness with a gaussian of the chosen radius and subtracts the blur from the original. What's left is the detail: positive on the light side of each edge, negative on the dark side. That detail, times the amount, goes back into the red, green, and blue of every pixel alike, which steepens edges without shifting colors. The threshold is taken off the detail first, so small differences like sensor noise get no boost and nothing changes abruptly at the threshold.

Tips

  • For photos at full size, start with a radius around 1 px and raise the amount until edges look crisp. Bright outlines around dark edges mean it's too strong.
  • Sharpen once, as the last step, after cropping and resizing.
  • In noisy photos, a small threshold keeps skies and skin smooth while edges still get sharper.