Summary
An image sharpener makes edges and fine detail look crisper by raising contrast along them. To sharpen a photo free and privately here, click Select Images, leave the Moderate preset on or choose another, drag the divider between Original and Sharpened to compare, and press Download. The work runs in your browser and nothing is uploaded, which the Network tab in DevTools will confirm.
The method is an unsharp mask: Sharpened = Original + (Original − Blurred) × Amount. It is applied to brightness only, so colours do not fringe, and only where the brightness difference is above the Threshold. Sharpening cannot invent lost detail, so it suits slightly soft photos. For heavy grain, run the image noise reducer first.
Table of Use: Photo Types and Starting Settings
| Photo | Amount / Radius / Threshold | Why |
|---|---|---|
| Everyday photo, slightly soft | Moderate: 100% / 1.5px / 5 | The default preset, labelled for most photos |
| Photo that was just made smaller | Strong: 150% / 2px / 10 | Shrinking softens edges, and this preset targets soft or resized images |
| Light touch-up on a sharp image | Subtle: 50% / 1px / 0 | Small radius, half strength |
| Bolder edges with clean areas kept | Wide Radius: 100% / 3px / 15 | A wider radius, with a higher threshold sparing smooth areas |
| Portrait with smooth skin | About 70–100% / 1–1.5px / 20–30 | A high threshold leaves low-contrast skin alone (a starting point, not a rule) |
| Batch where one picture needs more | Tick Custom settings for this image | That card gets its own sliders; the rest follow the main panel |
Features
- Unsharp mask with three controls: Amount 0–300%, Radius 0.5–10px and Threshold 0–50, plus four Quick presets: Subtle, Moderate, Strong and Wide Radius.
- Brightness-only sharpening that adds the same change to red, green and blue, so edges do not pick up coloured fringes. Transparent pixels do not darken the blur around them.
- Gaussian blur computed exactly up to a 3px radius, and approximated with three box passes above that.
- Before and after split view you can drag, with a slider underneath for keyboard use.
- Possible over-sharpening notice when more than 3% of pixels are pushed past pure black or white.
- Batch sharpening with no limit on images, optional per-image settings and one ZIP download.
Changes apply to every image that follows the main panel a moment after you stop moving a slider. The result keeps the original pixel size and, for JPG, PNG and WebP, the original format (other formats are saved as PNG); the file is named like photo_sharpened.jpg, and EXIF tags are not copied. A very large image can exceed what your browser can process, and its card then shows an error. To soften instead of sharpen, use the image blur tool.
How to Use the Image Sharpener
- Click Select Images or drop files on the upload area. Use Add More later for extra images.
- Wait for Sharpening… to finish; the first result uses the Moderate preset.
- Drag the divider between Original and Sharpened, or use the Before / after slider, to compare.
- Choose a preset under Quick presets or move Amount, Radius and Threshold. No sharpening (amount 0) sets Amount to zero.
- For one image, tick Custom settings for this image on its card.
- Press Download on a card, or Download All (ZIP) once several are ready. Clear all removes everything.
Who Can Use It
Photographers and bloggers can finish a shot after cropping with the image cropper, and shop owners can crisp up product pictures. Anyone who has shrunk a picture with the image resizer or made thumbnails with the thumbnail generator will notice the edges soften, and a pass here helps.
Fix exposure first with the brightness adjuster and contrast adjuster, or boost colour with the saturation adjuster. Then save space with the image compressor, or convert with the PNG to JPG converter.
FAQs
How do I sharpen an image online for free?
Click Select Images or drop files on the upload area. Each image is sharpened straight away with the Moderate preset (Amount 100%, Radius 1.5px, Threshold 5). Drag the Original and Sharpened divider to compare, pick another preset or move the sliders, then press Download, or Download All (ZIP) for several images. There is no account or watermark.
What is an unsharp mask?
An unsharp mask is a sharpening method that blurs a copy of the image, subtracts it from the original to isolate edge detail, and adds that detail back. Here the formula is Sharpened = Original + (Original − Blurred) × Amount, applied to brightness only, and only where the difference is larger than the Threshold. Smooth areas barely change.
What Amount, Radius and Threshold should I use?
Amount (0–300%) is the strength, Radius (0.5–10px) is the width of the edges enhanced, and Threshold (0–50) is the minimum brightness difference, on a 0–255 scale, before a pixel is sharpened. The presets are Subtle 50%, 1px, 0; Moderate 100%, 1.5px, 5; Strong 150%, 2px, 10; and Wide Radius 100%, 3px, 15. Raise Threshold to keep skin and sky smooth.
What does the over-sharpening warning mean?
After sharpening, the tool counts visible pixels pushed more than 8 levels past pure black or pure white. When that is over 3% of the image, a Possible over-sharpening notice appears, because such clipping usually means bright or dark halos along edges. Lower Amount or raise Threshold until the notice disappears.
Can sharpening fix a blurry photo?
Only slight softness. Sharpening raises contrast along edges that are already there; it cannot recover detail the camera never captured. A mildly soft photo can look crisper with the Strong preset, but badly out-of-focus or motion-blurred shots mostly gain halos. If the photo is also grainy, reduce the noise before you sharpen.
Should I sharpen before or after resizing?
After. Making an image smaller softens its edges, so resize first and sharpen as one of the last steps, following noise reduction, brightness, contrast and cropping. Sharpening also exaggerates grain, which is why a noisy photo should be denoised first. Enlarged images are softer still, but sharpening cannot add the missing detail.
Does sharpening change the file format or quality?
Pixel dimensions stay the same and the format is kept: PNG is saved losslessly, while JPG and WebP are saved at 95% quality. GIF, BMP, AVIF and other formats your browser can open are saved as PNG. Each file gets _sharpened added to its name, and JPG or WebP files may be slightly larger because they hold more fine detail.
Are my images uploaded when I sharpen them?
No. Reading, sharpening and saving all happen in your browser on your own device, which you can verify in the Network tab of DevTools. The tool never sends your images anywhere; the only file it loads on demand is its ZIP library, from this site, when you press Download All (ZIP). Clear all removes the images from memory.