Can it fix a blurry photo?

No. Sharpening raises contrast along edges that are already there. It makes a slightly soft photo look crisper; it cannot recover detail from a photo that was out of focus or blurred by movement.

Why is there a threshold?

Without one, sharpening also raises the small random differences between neighbouring pixels in flat areas such as sky and skin, which is noise. The threshold leaves differences below a set size alone.

How much for print or for a screen?

Judge at 1:1, not fitted to the window: press Z. For a screen, stop as soon as edges look clean; for a print, a little more is usually fine. If you see bright halos along edges, it is too much.

Every fix is made on this device.

Sharpen a photo

Opens in Detail with sharpening at 30. Check it at 1:1 with Z, then save.

Drop a photo in. Tap the spot you want gone.Click to browse. A copied picture pastes straight in. Nothing is sent.Spot · Heal stroke · Edge dab · Lift · Red-eye · Level — 6 marks, then it stops

Nothing to hand?

A drawing, not a photograph. Drag the seam: a speck of sensor dust in the sky, something dark pressed against the top border, the lower left corner sitting in shade — one tap each, and the one at the border only shows with the seam pushed right.

What is wrong with it?

Optional — the uploader works without it. It takes about five seconds and can save you a tap you would have undone.

What the sharpen does

Detail → Sharpen is an unsharp mask: it compares each pixel with a slightly blurred copy and pushes the difference, which raises contrast at edges. The radius is small and fixed, and a noise threshold keeps flat areas flat. The strength runs from 0 to 100 and opens here at 30.

Sharpening and smoothing are in the same step and can be used together: smooth skin a little, sharpen eyes and hair. Related: Reduce noise in a photo, Smooth skin in a photo.

Questions about sharpening

Can it fix a blurry photo?: No. Sharpening raises contrast along edges that are already there. It makes a slightly soft photo look crisper; it cannot recover detail from a photo that was out of focus or blurred by movement.
Why is there a threshold?: Without one, sharpening also raises the small random differences between neighbouring pixels in flat areas such as sky and skin, which is noise. The threshold leaves differences below a set size alone.
How much for print or for a screen?: Judge at 1:1, not fitted to the window: press Z. For a screen, stop as soon as edges look clean; for a print, a little more is usually fine. If you see bright halos along edges, it is too much.

Photographic visual for Sharpen Photo — Sharpen Photo