How to use Image Sharpen
- Choose one or more images.
- Set Strength (10–300%, starts at 80%).
- Set Radius (0.3–6 px, starts at 1 px). Small values sharpen fine texture; larger values add punch to bigger shapes.
- Set Threshold (protect smooth areas) (0–40, starts at 3).
- Pick Save as and Quality, press Apply, and download the files ending in -sharpened.
What it does and when to use it
Photos lose crispness when they are resized, scanned, or shot through a phone’s small lens. Sharpening makes them look clearer on screen. Typical cases are a product photo shrunk to 1000 px for a shop, a scanned print, or a screenshot that was scaled down. Run it after the Image Resizer, not before.
If the picture is soft on purpose, such as a portrait background, leave it, or go the other way with Image Blur. For blurred text in a photo of a document, extracting it with Image to Text may work better than sharpening.
How it works
Unsharp masking is a classic darkroom method. The tool makes a blurred copy of the picture (a Gaussian blur with your Radius), then, for each colour channel of every pixel:
new = original + Strength × (original − blurred)
Where the picture is flat, original and blurred are nearly the same and nothing changes. At an edge they differ, so the dark side gets darker and the light side lighter. If the difference is below Threshold, the pixel is left untouched. Everything runs in a Web Worker on your device.
Worked examples
We ran the tool’s function on a grey edge, 100 on the left and 150 on the right, and read the pixels around it. The slash marks the edge.
| Settings | Pixels across the edge |
|---|---|
| Default (80%, 1 px, 3) | 100, 86 / 164, 150 |
| Strength 200% | 100, 66 / 184, 150 |
| Radius 3 px | 98, 95, 92, 88, 82 / 168, 162, 158, 155, 152 |
With the default, only one pixel on each side moves, so the edge looks crisper without visible outlines. Strength 200% doubles the jump. Radius 3 spreads the effect wider, which reads as more contrast but can show halos.
Threshold protecting noise. A smooth patch with tiny variations (120, 122, 121, 119…) is unchanged at Threshold 3. At Threshold 0 the same patch becomes 119, 123, 121, 118…, so grain gets stronger.
Limits and tips
- Compression blocks in a low-quality JPEG get sharpened too; start from the best copy you have.
- Very high Strength can push pixels to pure black or white, which cannot be undone.
- The saved file is a new image without the original EXIF data.
- Compare results at 100% zoom; on a small preview most sharpening is invisible.
Frequently asked questions
Can sharpening fix an out-of-focus photo?
What are the light and dark outlines around edges?
What does Threshold do?
Should I sharpen before or after resizing?
Does it sharpen transparency too?
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