Chromatic aberration (also called achromatism, chromatic distortion, and spherochromatism) is a type of optical distortion where the edges of an image have a colored, blurry halo or fringe. The RGB color channels may be noticeably offset with respect to one another. In this respect it may sometimes resemble anaglyph.
Chromatic aberration arises in optics because a lens does not refract light of different wavelengths (colors) in precisely the same way (technically speaking, the index of refraction of a lens material varies depending on the wavelength). So if a camera is focused such that one color is perfectly focused, all other colors will be slightly out of focus. While it can minimized by various means, it can not be entirely eliminated.
Digital art has inherently zero chromatic aberration since it does not rely on real-world lenses at all, yet it is often intentionally simulated for artistic effect. In small amounts it can increase realism. In progressively greater amounts it can:
- create a sense of motion (similar to motion blur),
- convey a chaotic environment,
- indicate anxiety or paranoia,
- indicate mental derangement and/or mind control
Images with excessive chromatic aberration tend to give most people eyestrain and headaches if observed for too long.