Bring back crispness after resizing or a soft lens with an unsharp mask. Amount, radius and threshold, a live before-and-after, and nothing leaves your computer.
Runs an unsharp mask, the same method photo editors use. The tool makes a slightly blurred copy of your picture, subtracts it from the original to find the edges, and adds that difference back scaled by the amount. Edges get a touch more contrast, so the image reads as crisper, while flat areas are untouched. It works on the full-resolution pixels and the preview updates as you drag the sliders, with Space held down to peek at the original.
A 4000 × 3000 phone photo resized to 1600 px wide looks slightly soft, as every downscale does. Amount 40, radius 1 px, threshold 3 brings back the crispness of hair and brickwork without halos, and the JPEG at quality 92 comes out about 15 KB larger than the unsharpened version because there is a little more edge detail to encode. The same photo at amount 100 and radius 4 px shows white outlines around the roofline, which is the sign you have gone too far.
Use it after shrinking with Resize Image, on scans that came out soft, or on product photos that need a bit more bite for a listing. Sharpen last, after cropping, resizing and colour work, and before Image Compressor. Do not use it to rescue a picture that missed focus or has motion blur; it only strengthens edges that are already there. Noisy images get noisier, so run Remove Noise first or raise the threshold.
Amount is how much edge contrast is added; 25 to 50 covers most photos, 75 and up is for soft scans. Radius is the width of the edge band in pixels: 0.5 to 1.5 px sharpens fine texture on web-size images, 2 to 4 px adds punch to large prints. Threshold is the minimum difference a pixel must have from its blurred neighbour before it is touched; 3 to 10 protects skin and sky from grain, 0 sharpens everything.
Can sharpening fix a blurry photo? Only a slightly soft one. Sharpening raises contrast at edges that already exist; it cannot invent detail that motion blur or a missed focus destroyed. If the picture is clearly out of focus, no setting here will rescue it.
Why do I see bright outlines around things? Those are halos, the sign of too much amount or too wide a radius. Drop the radius to 1 or 1.5 px and the amount under 60, or raise the threshold so only strong edges are touched.
Should I sharpen before or after resizing? After. Shrinking an image softens it slightly, so resize first with Resize Image, then apply a light sharpen here. Sharpening first and then shrinking throws the effect away and can leave artefacts.
Is the image uploaded? No. The unsharp mask runs in your browser on a canvas. You can turn off the network after the page loads and it still works.
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