Sharpen
Sharpen edges by amount.
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About Sharpen
Sharpens edges by boosting each pixel against its four immediate neighbours, with an amount from 0.1 to 3, applied in your browser without the image being uploaded.
Resizing an image down almost always costs a little crispness, because the resampler averages neighbouring pixels together to produce the smaller one. Scans go soft for a related reason. And a photo shot at a slow shutter speed or through a cheap lens can sit very slightly off, in a way you notice on screen but cannot fix by pushing contrast. Sharpening is the usual patch for all three.
Each pixel is multiplied by 1 plus four times your chosen amount, then the four pixels directly above, below, left and right are subtracted at that same amount. The nine kernel values sum to 1, so overall brightness holds steady while local differences get exaggerated. Amount runs from 0.1, which is close to imperceptible, up to 3, which is aggressive. Edges gain the most because that is where neighbouring pixels differ most.
Sharpening adds no detail; it exaggerates the differences already present, including the ones you did not want. Sensor noise, JPEG blocking and compression fringing all get louder alongside the edges you were aiming at. Push past roughly 1.5 on a noisy photo and bright halos appear along high-contrast boundaries while flat areas turn gritty. A genuinely out-of-focus photograph cannot be rescued by this, or by anything else.
How to use Sharpen
- 1Drop your image onto the panel, or click to browse.
- 2Set Amount. Start near 0.5 and work up; above 1.5 most photos show halos.
- 3Click Apply preview, then check edges and flat areas rather than the middle of your subject.
- 4Click Download to save the sharpened PNG.
What it won't do
- A fixed 3×3 kernel, so there is no radius or threshold control the way a desktop unsharp mask has.
- Amplifies existing noise and JPEG artefacts along with the edges.
- Applies to the whole image; you cannot mask it to one area.
Common questions
How much sharpening is too much?
Halos are the tell. When a bright line appears along the dark side of a high-contrast edge, you have gone past useful. On a typical photograph that happens somewhere between 1.2 and 1.8 on this slider. Noisy images and heavily compressed JPEGs hit the ceiling much earlier, often below 0.8.
Can sharpening fix a blurry photo?
No. Sharpening increases local contrast at edges that already exist, which makes a slightly soft image look crisper. It cannot reconstruct detail that the lens or the shutter never captured. If the photo is genuinely out of focus, no amount of sharpening will recover the missing information.
Is this the same as an unsharp mask?
Not quite. A desktop unsharp mask blurs a copy of the image at a radius you choose and subtracts it, which gives you radius and threshold controls. This uses a fixed 3×3 convolution kernel that only looks at the four adjacent pixels, so the effect is tighter and there is one control instead of three.
Should I sharpen before or after resizing?
After. Downscaling averages neighbouring pixels together, which washes out sharpening applied beforehand and leaves you sharpening a second time to compensate — amplifying noise for no gain. The professional order is resize to final dimensions, sharpen for that size, then export. It also means the same source can be sharpened differently for a thumbnail and for print.
Related tools
Why this one doesn't upload your file
There is no server to upload to. This page is a static file, and the work happens in your browser using the same graphics and WebAssembly code that renders every other site you visit. Your file is read from disk into memory, processed, and handed back as a download. Once the page has loaded you can disconnect from the network entirely and it keeps working. The longer explanation