Field guide
Reading a sharpening halo
Sharpening increases contrast around an edge. When the created fringe becomes visible as a separate line, the settings have exceeded the image's scale.
01
A narrow bright rim and dark trough are the two sides of the same overshoot. Reducing amount lowers their contrast; reducing radius narrows their reach.
02
Inspect high-contrast boundaries such as branches against sky and dark text on paper. Low-contrast texture can hide a halo that later becomes obvious in print.
03
Do not judge a halo while zoomed far beyond one-to-one. Resampling the preview invents its own edge pattern and can exaggerate or conceal the actual pixels.
04
If the source was sharpened before, a second pass strengthens the existing fringe. Use an edge or acutance measurement as a warning and return to an earlier file when possible.