Online Tool Store
Image Sharpener
Sharpen a soft photo with a real unsharp mask, controlling amount, radius and threshold, and compare against the original. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Sharpening happens on your device — the photo is never uploaded.
No photo yet — choose one and the sharpened result appears here.
How it works
- Choose a photo. It is processed at full resolution on your device.
- Start from a preset, then adjust amount, radius, and threshold.
- Tick "show the original" to compare honestly before you commit.
- Download as PNG for lossless output, or JPG for a smaller file.
What an unsharp mask actually does
The name is confusing: it sharpens by using a blurred copy. Subtracting the blur from the original leaves only the fine detail, and adding that detail back — amplified — increases contrast exactly where edges already are:
detail = original − blurred
result = original + amount × detail // only where |detail| > threshold
Take a soft edge where a pixel reads 200 and its blurred version reads 170, so the detail is +30. At 50% amount the pixel becomes 215; at 80% it becomes 224; at 150%, 245. On the dark side of the same edge the detail is −30, so those pixels move down instead — 100 becomes 76 at 80%. Light sides get lighter and dark sides get darker, which is what the eye reads as sharpness.
Notice what this means: no new detail is created. The tool is redistributing contrast that is already present, which is why it helps a soft photo and does nothing for one that is genuinely out of focus.
Why threshold matters more than people expect
Without a threshold, sharpening amplifies everything — including sensor noise in flat areas. A pixel at 128 whose neighbourhood averages 126 has a detail value of just 2, which is noise rather than an edge:
threshold 0 → 128 becomes 130 // noise amplified
threshold 3 → 128 stays 128 // left alone
That is why a small threshold keeps skin, sky, and shadow smooth while still sharpening the eyelashes and the brickwork. The status line under the sliders shows what proportion of pixels your current threshold treats as edges, so you can see the effect of moving it.
One implementation detail worth mentioning: the alpha channel is deliberately left untouched. Sharpening transparency produces visible fringes around a cut-out subject, which is rarely what anyone wants.
FAQ
Is my photo uploaded anywhere?
No. The sharpening runs on a canvas inside this page, at full resolution, and the result only leaves your device if you download it.
Can it fix a genuinely blurry photo?
No, and nothing honestly can. Sharpening increases the contrast at edges that are already in the image — it does not recover detail that was never captured. It works well on softness from a lens, a resize, or a scan, and it cannot rescue motion blur or a missed focus.
What do the three controls actually do?
Amount is how much the detail is amplified. Radius is how wide a transition counts as an edge — small for fine texture, larger for soft general softness. Threshold is the cutoff below which differences are ignored, which is what keeps smooth skin and clear sky from turning grainy.
Why do light halos appear around edges when I push it?
Because the boosted values run past what the image can hold and get clipped. Take a pixel at 250 next to one at 200 and apply 300%: the maths asks for 400, which clamps to 255 — a flat white rim. That is the classic over-sharpened look, and the fix is less amount or a smaller radius.
Which preset should I start from?
"Web resize" if you have just scaled a photo down, since downscaling always softens it slightly. "Subtle" for a photo that is nearly right. "Strong" mainly for scans and documents, where crisp edges matter more than natural texture.
Should I sharpen before or after resizing?
After. Resizing re-samples every pixel and softens the result, so sharpening first means the softening is applied to your sharpened edges. Sharpening last, at the final size, is the order every image workflow recommends.
How we compare
| Feature | Online Tool Store | Upload-based photo sites | Photoshop / Lightroom |
|---|---|---|---|
| Your photo never leaves your device | ✓ | ✗ | ✓ |
| Real amount / radius / threshold control | ✓ | Usually one "sharpen" slider | ✓ |
| Full resolution, no watermark or sign-up | ✓ | Free tiers often limit both | Paid licence |
| Honest before/after comparison | ✓ | Sometimes | ✓ |
| AI upscaling that invents new detail | ✗ | ✓ | ✓ |
| Masking, so you sharpen only part of the image | ✗ | ✗ | ✓ |
Best for the everyday case: a photo that went soft after resizing, a scan that needs crisping, a product shot that is nearly there — with the three controls that actually matter and nothing uploaded. It sharpens the whole frame and invents nothing; selective masking and AI detail generation are elsewhere.