Chromatic Aberration or color fringing is an optical problem which occurs when a lens is not able to bring all wavelengths of color to a common focal plane or when the wavelengths are focused at different positions in the focal plane. In uncorrected lenses, the result is colored fringes in the images produced.
This phenomenon is caused by lens dispersion in which different colors of light travel at different speeds while passing through a lens, causing a blurred image. Noticeable colored edges may also appear around objects, mainly in high-contrast situations.
Since the refractive index for each wavelength is different in lenses, two types of Chromatic Aberration result: Lateral Chromatic Aberration and Longitudinal Chromatic Aberration
Longitudinal Chromatic Aberration (LoCA) occurs when different wavelengths of color fail to converge at a common point after passing through a lens. A lens with this problems may show fringing around objects throughout the image including center. It can be reduced by stopping down the lens.
Lateral Chromatic Aberration results when different wavelengths of the color incident at an angle focus at different positions along the same focal plane. This type does not show up in the center. It is only visible towards the corners of the image in high-contrast areas. It can be eliminated or reduced in post-processing software.
In many lenses, both longitudinal and lateral chromatic aberrations are present at the same time and can only be removed by the above techniques. Chromatic aberration, however, remains problematic in most prime and zoom lenses. Many modern DSLRs incorporate special in-camera post-processing techniques to reduce chromatic aberrations.
Johnson, Micah K., and Hany Farid. “Exposing digital forgeries through chromatic aberration.” Proceedings of the 8th workshop on Multimedia and security. ACM, 2006.
Kidger, Michael J. “Fundamental optical design.” SPIE, 2001.