What sharpening does to a picture
Sharpening makes edges look crisper by increasing the contrast between each pixel and the pixels right next to it. Where a dark area meets a light area, the dark side gets a little darker and the light side a little lighter, and the eye reads that as a clearer edge.
The tool here uses a small 3 by 3 convolution filter. For every pixel it looks at the four neighbors directly above, below, left and right, subtracts a share of them, and adds that back to the pixel itself. The strength slider controls how large that share is. Higher values exaggerate edges more.
Sharpening does not add information. It only changes how existing detail is emphasized, so a photo that is truly out of focus or smeared by camera shake will not become sharp, it will just gain harsher edges.
When sharpening is worth doing
Photos that look slightly soft are the best candidates. Common causes are a small amount of lens softness, an image that was scaled down and lost crispness, or a screenshot that was resampled by a chat app. A modest amount of sharpening can bring back the feeling of detail without any other editing.
It also helps with text in scanned or photographed documents, where letter edges look faint. After you shrink a large image with the resizer, a light sharpening pass is a common last step because downscaling tends to soften fine lines.
It is a poor fix for heavy blur, noisy night photos, or very low resolution images. Sharpening amplifies noise along with detail, so grainy photos can look worse afterward.
How to sharpen an image with this tool
- Drop an image onto the upload area, or click it to choose a file from your device. Any image your browser can open will work.
- The original appears on the left with its file name, size and pixel dimensions.
- Move the Sharpen strength slider. It runs from 0.1 to 2.0 and starts at 0.5.
- Click Sharpen. The result appears on the right.
- Compare the two previews. If it looks too harsh, lower the slider and click Sharpen again, since each run starts from your original file.
- Click Download to save the result. The file is a PNG named after your original with "-sharpen" added, for example
photo-sharpen.png.
Everything runs in your browser on a canvas, so the image is never uploaded.
Tips and limits
Start low. Values around the default are usually enough, and the top of the slider tends to produce bright halos along edges and a crunchy, over-processed look.
Because the output is always a PNG, a sharpened JPG will often come out larger than the original. If file size matters, run the result through the image compressor afterward.
The filter works on color channels only and keeps transparency unchanged. Very large images take longer, because the filter visits every pixel in your browser, so expect a short pause on big photos. Always keep your original, since sharpening cannot be undone once you overwrite the file.