simultankontrast

Simultankontrast, or simultaneous contrast, is a perceptual phenomenon in color vision in which the perceived color and brightness of a region are affected by the colors surrounding it. In practice, a patch of the same grey or hue can look lighter when placed against a dark surround and darker against a light surround, even though the patch itself has unchanged physical properties.

The effect arises from how the visual system processes color and lightness through opponent channels and lateral interactions in the retina and visual cortex. Surrounding colors bias the responses of color-opponent neurons, as well as neurons involved in brightness processing, leading to shifts in the perceived hue and luminance of the central area. It is a cornerstone example of how context alters appearance rather than reflecting changes in the stimulus itself.

Common demonstrations include a neutral gray appearing lighter on a dark background and darker on a light background, or warm and cool surrounding colors causing adjacent areas to seem to shift in hue. The phenomenon is distinct from afterimages, which are temporal rather than spatial effects, and from other contrast types described in color theory.

Historically, simultaneous contrast was described and systematized in the 19th century as part of the study of color harmony, most notably by Charles Chevreul. Today it remains a fundamental principle in art, design, and perception research, used to achieve visual separation, depth, or vibrancy by manipulating contextual color relationships.