chromatism

Chromatism is a term derived from the Greek chroma (color) used in several fields to denote color-related properties or phenomena. In optics and imaging, it most often refers to chromatic aberration, the failure of a lens to focus all wavelengths at the same point. Chromatic aberration arises because the refractive index of lens material varies with wavelength, causing different colors to come to focus at different distances. This results in color fringes around high-contrast edges and a loss of sharpness, particularly toward the image periphery. Two main forms are axial (longitudinal) chromatism, where colors focus at different distances along the optical axis, and lateral (transverse) chromatism, where colors focus at different positions across the image plane.

Correction and management are central to optical design. Achromatic lenses combine two materials to bring two wavelengths into common focus, reducing axial chromatism; apochromatic designs extend correction to three wavelengths. Other approaches include low-dispersion glass, special coatings, aspheric elements, and computational post-processing.

In color science and display technology, chromatism can describe wavelength-dependent sensor response or color rendering under different illuminants, contributing to phenomena such as metamerism, where colors match under one light but not another. The term also appears in discussions of color reproduction in photography and printing, where maintaining consistent color across devices addresses chromatism-like issues.

In the arts and humanities, chromatism is sometimes used to discuss the use of color emphasis or chromatic contrast in composition, though the term is less common today and more often described with terms such as color theory or chromaticism.