Sharpen a photo without bright rims

Every sharpening control on every editor does the same thing underneath: it finds where brightness changes quickly and steepens the change. That is why it helps a picture that is merely a little soft and does nothing for one that is out of focus. This page gives you the three numbers that control the steepening and one number that tells you when it has gone too far.

The built Sharpen slider on every other page is a one-pixel version of the same operation. Here the advanced controls open in its place, seeded from it: the slider's 100 corresponds to an amount of 160 per cent at a radius of 1.0 px. While the advanced controls are on, the simple slider does nothing, so the two never stack.

A halo is what over-sharpening looks like: a thin bright line on the light side of an edge and a dark one on the other. The meter measures exactly that — how far the sharpened brightness pokes beyond the darkest and brightest values near each strong edge before sharpening. It warns and never blocks.

A large radius on a small picture outlines every object; a tiny radius on a large, soft picture does nothing visible. As a rule, start at 1.0 px for pictures up to about 2,000 px wide and move towards 2 px for bigger, softer ones. Raise the threshold before you lower the amount if the sky, skin or a wall starts to look sandy: that grit is noise being sharpened, and threshold is what tells the mask to ignore it.

• Sharpening cannot rescue motion blur or missed focus: the detail is spread across many pixels and an edge filter does not gather it back.
• The automatic pass never sharpens on its own; everything here is a visible, movable control.

Does sharpening add detail?

No. Sharpening adds contrast across edges that are already in the picture, which makes them read crisper at viewing distance. It cannot put back texture that was never recorded; for a frame that is slightly soft rather than under-sharpened, the unblur route runs a deconvolution instead.

What do amount, radius and threshold do?

Amount is how much of the difference between the picture and a blurred copy is added back. Radius is the width of that blur, so it decides which size of edge is affected: about 1 px for fine detail, 2–3 px for a soft, large picture. Threshold leaves differences smaller than that many levels alone, which keeps smooth skin and sky from turning gritty.

What is the halo meter measuring?

After each change it compares the sharpened brightness with the local range of the unsharpened picture around every strong edge, and reports how far the result overshoots that range at the 99th percentile. A few levels is invisible; past about ten levels a bright rim is visible at 100 per cent.

Why only brightness?

Because sharpening the colour channels separately draws coloured fringes along high-contrast edges. Sharpening brightness alone gives the same crispness with none of them.

Is the preview what will be saved?

The stage shows a working copy at up to 2,048 px; the loupe and the saved file run the same stages on the full-resolution picture. The halo reading comes from the working copy, so check the loupe at 1:1 before you save.

• Image clarity enhancerClarity, sharpening and grain checked at 1:1 in a loupe on the busiest patch before you save.
• Unblur imageA measured deconvolution for slight softness — and a plain warning when the blur is motion.
• Denoise photoGrain measured first, colour noise removed, luminance grain reduced to taste, fine detail kept.
• Clarity and sharpening solve different problemsSeparate midtone local contrast from edge acutance before enhancing a photograph.