Sharpen Image
Sharpen an image or video with an unsharp mask: set how hard edges are boosted, how wide, and what noise to leave alone. A fix for soft photos, in your browser.
How does sharpening work?
This tool uses an unsharp mask, the same method as the filter of that name in photo editors. It makes a blurred copy of the picture and subtracts it from the original. What's left is the fine detail, the parts that change quickly, and that gets added back on top, scaled up.
So an edge between a dark and a light area gets a little darker on its dark side and a little lighter on its light side. Nothing new is invented, but the eye reads the stronger edge contrast as crisper detail. The name comes from the darkroom, where printers sandwiched a blurred negative with the original to do the same thing.
What Amount, Radius and Threshold do
Amount is how hard the detail gets pushed, and it opens at 3. Radius is how wide the blur is, so how far around each edge the boost reaches, and it opens at 5. Threshold leaves alone any difference smaller than its value, which keeps flat areas such as skin and sky from turning gritty.
The presets cover the usual cases. Subtle drops Amount to 1 for a light touch-up. Wide sets Radius 15 and Amount 2, which brings out texture and depth more than fine edges. Clean sets Threshold 0.05, so anything under about 13 steps out of 255 is left untouched, and then pushes Amount to 4 on what remains.
Can sharpening fix a blurry photo?
It can fix a soft one, not a blurry one. A picture that's slightly out of focus, softened by resizing or by a cheap lens still has its edges, only gentle, and sharpening steepens them again. Detail that a missed focus or a shaky hand smeared away isn't in the file anymore, and pushing harder just draws bright and dark outlines around the blur.
Those outlines are halos, and they're the sign you've gone too far. Zoom in on a high-contrast edge, like a dark roofline against the sky. If a white rim runs along it, lower Amount or Radius until it fades.
When should you sharpen?
Last. Every edit after sharpening can soften the picture again, and shrinking it to a smaller size, as the tools in the Image Tools hub do, softens it most of all. Resize first, then sharpen at the size people will see.
Small pictures need a small Radius, around 1 to 2, or the boost spreads into a halo wider than the detail itself. Video is the other case for caution. Sharpening boosts noise along with detail, and since the noise changes on every frame, it shows up as a shimmer, so give a clip some Threshold.
Sharpening and blurring in one picture
The two go well together. Blur Image can soften a background while this tool crisps up the subject in front of it, and the contrast between them makes the subject stand out more than either would alone. Use the Mix mask on the sharpen to keep it to the subject's area.