Image Sharpener
Bring back crisp detail in soft photos, scans and screenshots. Adjust a true unsharp mask with amount, radius and threshold and drag the before/after slider to see the difference.
Preset
Unsharp mask
Save
How to use the Image Sharpener
- Add a photo by dropping it on the box, choosing a file or pasting with Ctrl+V.
- Pick a preset such as Standard, or set amount, radius and threshold yourself.
- Drag across the picture or use the Compare slider to see before and after; tick Actual pixels to judge fine detail.
- Press Sharpen image to re-run with the current settings if needed (the preview also updates live).
- Choose a format and press Download to save the sharpened image at full resolution.
The unsharp mask formula
For every pixel the tool computes a Gaussian-blurred value and then:
sharpened = original + amount × (original − blurred), but only where |original − blurred| ≥ threshold.
The blur uses a Gaussian kernel with standard deviation σ equal to the radius, sampled out to 3σ on each side and normalised so the weights add up to 1. It is applied first horizontally and then vertically, which gives exactly the same result as a 2D Gaussian but is much faster.
Worked example: at a hard edge between a gray of 100 and a gray of 150, with radius 2 px and amount 100%, the blurred value just left of the edge is about 120 (the blur pulls in some of the brighter side). The pixel becomes 100 + 1 × (100 − 120) ≈ 80, and the pixel just right of the edge rises to about 170. The edge now jumps by about 90 levels instead of 50, so it looks crisper.
Recommended settings
| Image | Amount | Radius | Threshold |
|---|---|---|---|
| Web photos and social media | 80–150% | 0.8–1.5 px | 2–4 |
| Portraits (keep skin smooth) | 80–120% | 1–2 px | 6–10 |
| Landscapes and architecture | 150–250% | 1–2 px | 0–3 |
| Slightly out-of-focus shots | 80–150% | 3–6 px | 1–3 |
| Upscaled or scanned images | 100–200% | 1.5–3 px | 2–5 |
| Before printing | 150–250% | 1.5–2.5 px | 2–4 |
Tips for natural-looking sharpening
- Resize first, sharpen last. Downscaling softens an image, so sharpen after resizing to the final size.
- Judge at 100%. Tick Actual pixels to see real detail; a zoomed-out preview hides halos and noise.
- Raise the threshold for noisy photos so the grain in smooth areas is not amplified.
- Keep brightness-only mode on to avoid colour fringes along high-contrast edges.
- Avoid sharpening twice. Repeated sharpening quickly creates harsh, crunchy edges.
Frequently asked questions
Can this tool unblur any photo?
Sharpening increases contrast along edges, which makes slightly soft, out-of-focus or upscaled photos look much crisper. It cannot recover detail that was never captured, so heavy motion blur or a tiny, very blurry image will only improve a little.
What is an unsharp mask?
It is the classic sharpening method from film darkrooms. The image is blurred with a Gaussian blur, the blurred copy is subtracted from the original to find the edges, and that edge detail is added back on top, multiplied by the amount.
What do amount, radius and threshold do?
Amount sets how strong the edge contrast becomes. Radius sets how wide the halo around each edge is: small values (0.5 to 1.5 px) sharpen fine texture, larger ones (3 to 6 px) add punch to soft photos. Threshold leaves areas alone where the difference is smaller than that many brightness levels, which keeps skin and skies smooth.
Why do I see bright or dark halos?
Halos appear when the amount or radius is too high. Lower the amount first, then the radius. Keeping Sharpen brightness only switched on also prevents coloured fringes.
Does the image size change?
No. The sharpened image has exactly the same width and height as the original. Choose PNG for lossless output, or JPG or WebP for smaller files.
Are my photos uploaded?
No. The unsharp mask runs on your device in a background worker inside the browser, so your images never leave your computer or phone.