haloing

Haloing is the appearance of a circular glow around a bright light source or high-contrast edge. It is a perceptual or optical phenomenon that can occur in nature, in human vision, or in digital imagery. Haloing results from light being scattered, diffracted, or reflected in a way that produces a surrounding ring or arc.

In photography and display technologies, haloing is an optical or processing artifact. It can arise from lens flare, diffraction, sensor bloom, or aggressive sharpening, and may appear as a ring or halo around bright points. Mitigation includes using better lens coatings, stopping down the aperture, avoiding overexposure, and applying careful post-processing.

In atmospheric science and astronomy, halos around the Sun or Moon are called halos. They form when light passes through ice crystals in the atmosphere, producing refraction and reflection patterns such as the common 22-degree halo, parhelia (sundogs), and light pillars. The specific pattern depends on crystal shape, orientation, and atmospheric conditions; halos can indicate weather changes.

In human vision and ophthalmology, halos can be perceived around lights, especially at night. They may result from optical imperfections in the eye (cataracts, corneal edema, dry eye) or from diffraction by the eye’s optical media, and can be worsened by glare sensitivity or larger pupil size.

In image processing, haloing can describe ring-like artifacts near sharp edges after sharpening, deconvolution, or compression. Reducing haloing typically requires careful restoration, restrained processing, or improved acquisition techniques.