WeberKontrast

WeberKontrast, often written Weber-Kontrast and referred to in English as Weber contrast, is a measure used in vision science and psychophysics to quantify the perceptual difference between a small target and its uniform background. It is particularly applicable when the background luminance is greater than or comparable to the target luminance.

The Weber contrast is defined as C_W = (I_t − I_b) / I_b, where I_t is the luminance of the target and I_b is the luminance of the background. The value is positive when the target is brighter than the background and negative when the target is darker. The magnitude of C_W describes the relative change in luminance that is detectable against the background, aligning with the idea that perceptual sensitivity scales with background brightness in many conditions.

In practice, Weber contrast is used to design and interpret experiments on contrast sensitivity, to calibrate display and imaging systems, and to assess visibility of objects against varying backgrounds. It is especially relevant for tasks involving small or isolated objects on relatively uniform surroundings. Weber contrast is related to Weber’s law, which posits that the just noticeable difference in stimulus intensity is proportional to background intensity, making C_W a practical, perceptually meaningful metric for many visual situations.

Compared with other contrast measures, such as Michelson contrast, Weber contrast is most appropriate for small targets on uniform backgrounds and can be limited by background nonuniformity, spatial frequency, and chromatic factors. The term derives from Ernst Weber and remains standard in German-language literature as Weber-Kontrast.