How to Sharpen a Photo
Sharpening does not add detail — it makes existing detail easier for the eye to read, by increasing contrast along the edges that are already in the image. The technique is called an unsharp mask, and despite the confusing name it is what every professional editor uses. This tool implements it properly, in luminance only and with a threshold control, which is what separates a crisp result from a noisy, over-processed one.
Upload your photo
Processing happens at full resolution inside your browser. Nothing is uploaded.
Pick a preset or tune it
Start with Standard, or choose a preset matched to what you are sharpening, then adjust the three controls.
Compare and download
Hold the compare button to check against the original. Zoom in - sharpening is judged at full size, not thumbnail size.
The Three Controls, and Why Threshold Matters Most
Amount is how hard the effect is pushed, and it is the one everyone reaches for. Radius decides what counts as an edge: a small radius picks out fine texture like eyelashes and fabric weave, while a larger one works on broader transitions and suits genuinely soft images. Above about 2px you start producing visible bright halos along contours, which reads as obviously edited.
Threshold is the control that separates good sharpening from bad, and it is the one most tools hide. Every photo contains sensor noise in its flat areas — a clear sky, a plain wall, skin. Without a threshold, sharpening amplifies that noise into visible grain along with the detail you wanted. Setting a threshold tells the algorithm to ignore differences below a certain size, so flat areas stay smooth while real edges still get their contrast boost. For portraits and high-ISO shots, raise it. For flat graphics and screenshots, which have no noise at all, drop it to zero.
One technical note worth knowing: this tool sharpens the luminance channel only. Sharpening each colour channel separately — which naive implementations do — amplifies colour noise and produces coloured fringes along edges. Working on brightness and carrying the colour information through unchanged avoids both problems entirely.
Common Situations This Tool Solves
A photo that came out slightly soft
Marginal focus misses and camera shake at slow shutter speeds leave images that are almost sharp. Modest sharpening often rescues them completely.
Restoring bite after resizing
Every downscale softens an image slightly - it is unavoidable in the maths of resampling. A light sharpen afterwards is standard practice for web images.
Screenshots and flat graphics
Text and interface elements sharpen extremely well because they have hard edges and no noise. Drop the threshold to zero and use a small radius.
Scanned documents and old photos
Scanning softens everything. Sharpening restores legibility in text and definition in faces, though old prints benefit from a higher threshold to avoid emphasising paper grain.
Frequently Asked Questions
How do I sharpen a photo online for free?
Upload it, pick a preset or adjust the three controls, and download. Free, no signup, no watermark and full resolution output.
Can this fix a blurry photo?
Only partly, and it depends on the blur. Slight softness responds very well. Genuine motion blur or a badly missed focus has destroyed information that no tool can invent back.
What is an unsharp mask?
A blurred copy of the image is subtracted from the original to isolate the edges, and those edges are then boosted. The name comes from the darkroom technique it imitates.
What does the threshold control do?
It ignores differences below a set size, so flat areas like sky and skin keep their smoothness instead of having sensor noise sharpened into visible grain.
What settings should I use for portraits?
A modest amount, a small radius and a higher threshold. Skin sharpens badly - it emphasises pores and noise - so protect it and let the eyes and hair take the effect.
What settings for screenshots or text?
Set the threshold to zero and use a small radius with a higher amount. Flat graphics have no noise to protect and hard edges that respond very well.
Is my photo uploaded to a server?
No. All processing happens on a canvas inside your browser. Your photo is never uploaded, stored or seen by anyone.
Why do I see white outlines around objects?
That is halo, caused by too much amount or too large a radius. Reduce both - halos are the clearest sign of oversharpening.
Should I sharpen before or after resizing?
After. Resizing softens the image, so sharpening first means the effect is partly undone. Sharpen as the final step before export.
Does it work at full resolution?
Yes. Every original pixel is processed - the on-screen preview is only scaled to fit your display.
Why does the file size change?
Sharpening adds high-frequency detail, which JPEG compresses less efficiently. A sharpened file is often slightly larger than the original.
Is this sharpening tool really free?
Completely free, with no limits, no watermark, no signup and no premium wall. Everything runs in your browser.
Last updated: July 19, 2026 · FlipMyFormat Image Sharpener
Written and maintained by the FlipMyFormat team