Softonic

Image Sharpen Filter

Step 1 / 3 Sharpen amount

A phone photo at the long end of the zoom, a JPEG that has been compressed once too many times, or a resized image that has lost edge clarity all benefit from targeted sharpening. This filter uses the same unsharp-mask algorithm as Photoshop and Lightroom, amount, radius and threshold, so you can recover apparent detail without producing the halo artefacts that cheap sharpening causes.

How to sharpen an image

  1. 1

    Upload an image

    JPG, PNG or WebP.

  2. 2

    Set amount

    50-100% is standard; higher values show halos around edges.

  3. 3

    Set radius

    0.5-2 px for subtle sharpening, 3-5 px for emphasising larger edges.

  4. 4

    Set threshold

    Higher threshold excludes smooth areas (skin, sky) from sharpening.

  5. 5

    Export

    Preview at 100% zoom: sharpening always looks stronger at zoomed-in views.

Unsharp mask, properly tuned

Unsharp masking is counter-intuitively named, it blurs the image, subtracts the blurred version from the original to isolate edges, and adds a weighted copy of those edges back to the original.

The three parameters

Parameter What it controls Typical value
Amount How strongly the edge map is added back 50-150%
Radius How wide the edge is considered to be 0.5-2 px for web, 1-3 px for print
Threshold Minimum contrast required for sharpening to apply 0-5 (higher = only strong edges)

Sharpening by image type

  • Portrait: radius 1 px, amount 60%, threshold 5, keeps skin smooth.
  • Landscape: radius 1.5 px, amount 100%, threshold 0, crisp trees and rocks.
  • Architectural: radius 0.8 px, amount 140%, threshold 0, clean lines.
  • Product shot: radius 1 px, amount 120%, threshold 0, tight edges.
  • Text scan: radius 0.5 px, amount 200%, threshold 0, maximum edge boost.

Halos and over-sharpening

Amount values above 200% almost always produce visible halos, a bright edge on one side of a sharp transition, a dark edge on the other. Check at 100% zoom before exporting. If halos are visible, drop the amount and increase radius slightly.

Workflow

  1. Finish all other edits first (crop, colour, tone), sharpening is always the last step.
  2. Sharpen for output size: a photo destined for 800 px wide needs lighter sharpening than the same photo at 3000 px.
  3. For print, sharpen slightly more than you would for screen, ink on paper softens edges.

Frequently Asked Questions

Halos from over-sharpening. Drop the Amount value or raise the Threshold so only strong edges get boosted. Halos are almost always a sign the algorithm was pushed too hard.

Only partially. Sharpening increases local contrast at edges, which creates the impression of more detail. It cannot add information the lens or motion blur did not capture. For blurry shots, the best outcome is a more pleasant-looking image, not true recovery.

On images with smooth areas you do not want sharpened, skin in portraits, sky in landscapes. Threshold of 4-8 tells the algorithm to skip subtle variation and only sharpen real edges.

Yes, noticeably. Sharpened images have more high-frequency content, which JPG compresses less efficiently. Expect 10-20% size increase for matching quality.

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