Webercontrast

Webercontrast, commonly referred to as Weber contrast, is a measure used in vision science to quantify the detectability of a luminance stimulus against a uniform background. It is defined as C_W = (L_s − L_b) / L_b, where L_s is the luminance of the stimulus and L_b is the luminance of the background. The sign indicates whether the stimulus is brighter or darker than the background, though many studies report the absolute value when only detectability matters.

This measure is particularly applicable when the background luminance dominates the scene and the stimulus is small relative to the background. It aligns with Weber’s law for near-threshold detection and is widely used in psychophysics, ophthalmology, and display engineering to characterize contrast sensitivity and legibility. Weber contrast is often used for letters on screens, printed material, and other simple targets where the background remains approximately uniform.

By contrast, Michelson contrast is more appropriate for patterns with substantial luminance variation, defined as (L_max − L_min)/(L_max + L_min). Weber contrast and Michelson contrast yield similar results only under specific conditions; they are not interchangeable for all visual scenes.

Limitations include the assumption of a uniform background and stable adaptation state; real-world scenes with nonuniform lighting or color can reduce the applicability of simple C_W calculations. Extensions exist for chromatic or color-dependent contrast and for non-luminance-based stimuli.

Historically, the concept is named after Ernst Heinrich Weber, whose work on sensory thresholds laid foundations for this and related measures in perceptual science.