Sharpen Image

How it works

Each pixel is compared against its immediate neighbors and pushed further from their average — the standard "unsharp mask" technique. It can't recover detail that was never captured (like out-of-focus blur), but it can make edges look more defined.

Concretely, a 3×3 filter sets each pixel to five times its own value minus the pixels directly above, below, left and right of it. The weights add up to one, so flat areas keep their exact color while pixels at an edge are pushed apart, which is what reads as extra crispness. Red, green and blue are sharpened and transparency is left untouched.

When it helps

It works best on photos that are slightly soft, on images that were scaled down, and on scans or screenshots with blurred text edges. Sharpen after resizing rather than before, because resizing softens an image again.

Limits

The strength is fixed and there is no slider, so you get one standard pass. Sharpening also boosts noise and JPEG artifacts, and on hard edges it can leave a thin light or dark halo, so it is best used once. It can't repair motion blur or a missed focus. A PNG stays a PNG, other formats are saved as JPEG, and the work happens in your browser without uploading the file.

What you get

The sharpened image has the same pixel dimensions as the original and downloads as a new file, leaving your original untouched. Each pixel is processed in your browser, so a very large photo can take a few seconds.