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Real unsharp mask · before/after toggle

Sharpen a photo

This runs the same unsharp-mask maths that photo editors use, with the three controls that matter, and it tells you plainly which kinds of blur it cannot undo.

Amount, radius, thresholdBefore/after toggleNo uploadPNG export

Load a photo and sharpen it

Processing happens on this page; the file is never uploaded.

One image at a time
Download PNG

Sharpening raises contrast at existing edges. It cannot undo motion blur or a missed focus — no tool can.

How it works

  1. The image is drawn to a canvas (long edge capped at 1800 px) and its pixels are read out.
  2. A separable box blur of your chosen radius produces a soft copy. The difference between original and blur is the detail layer.
  3. That detail layer is multiplied by the amount and added back — the classic unsharp mask. The threshold skips differences smaller than the value you set, so flat sky and skin do not turn grainy.
  4. Export is PNG, so the sharpening is not immediately undone by JPEG compression.

What it will never do

  • It cannot recover detail that was never recorded. Motion blur, a missed focus and heavy upscaling are lost information — sharpening only raises local contrast around edges that already exist.
  • There is no AI, no invented pixels and no “enhance” magic. What you see is arithmetic on your own pixels.
  • Nothing is uploaded. The image never leaves the tab.

Questions

Can this fix an out-of-focus photo?

No, and neither can any honest sharpening filter. Out-of-focus and motion blur destroy information. Unsharp mask increases contrast at edges, which makes a slightly soft photo look crisper — it does not reconstruct what the sensor never captured.

What do the three sliders do?

Amount is how strongly the detail layer is added back. Radius is how wide the edge halo is — small for fine detail, larger for soft images. Threshold ignores small differences so noise and smooth areas stay smooth.

Why does the image get halos?

That is over-sharpening: too much amount with too large a radius. Lower the amount first, then the radius. The before/after toggle makes it obvious.

Sharpening photos on iPhone regularly?

Unblurry is optional — this free tool runs entirely in your browser and works without it. Check the app’s current App Store listing for exact features, pricing and availability before downloading.

View Unblurry on the App Store