luminancecontrast

Luminance contrast refers to the difference in brightness between two areas of a visual scene as perceived by the human eye. It is a fundamental cue for detecting edges, reading text, and recognizing objects. Luminance contrast depends on scene luminance, surface properties, lighting conditions, viewing geometry, and the nonlinear response of both display systems and the visual system.

Two standard measures are Michelson contrast and Weber contrast. Michelson contrast is defined as (Lmax − Lmin) / (Lmax + Lmin) and is suitable for patterns with alternating bright and dark regions of similar size. Weber contrast is defined as (L − L0) / L0 and is used when a small target stands out against a large background. Luminance values are typically expressed in candelas per square meter (cd/m2). In practice, readability and accessibility are often quantified using contrast ratios based on relative luminance, as in accessibility guidelines like WCAG, which compute ratios from the higher and lower relative luminances of two colors.

Applications and considerations emphasize practical use and perception. In display design and typography, appropriate luminance contrast supports visibility across diverse environments and viewing conditions. For accessibility, maintaining sufficient contrast under varying ambient light and device settings is essential, often requiring gamma correction and careful color management to achieve perceptually uniform luminance. In computer vision and image processing, luminance channels commonly drive edge detection and texture analysis due to their strong link to perceived brightness.