Contrast in visual perception is the difference in appearance of two or more parts of a field seen simultaneously or successively (hence: brightness contrast, lightness contrast, colorcontrast, simultaneous contrast, successive contrast, etc.).
Contrast in physics is a quantity intended to correlate with the perceived brightness contrast, usually defined by one of a number of formulae (see below) which involve e.g. the luminances of the stimuli considered, for example: ΔL/L near the luminance threshold (known as Weber contrast), or LH/LL for much higher luminances.A contrast can also be due to differences of chromaticity specified by colorimetric characteristics (e.g. the color difference ΔE CIE 1976 UCS).
Visual information is always contained in some kind of visual contrast, thus contrast is an essential performance feature of electronic visual displays.
The contrast of electronic visual displays depends on the electrical driving (analog or digital input signal), on the ambient illumination and on the direction of observation (i.e. viewing direction).
The "luminance contrast" is the ratio between the higher luminance, LH, and the lower luminance, LL, that define the feature to be detected. This ratio, often called contrast ratio, CR, (actually being a luminance ratio), is often used for high luminances and for specification of the contrast of electronic visual display devices. The luminance contrast (ratio), CR, is a dimensionless number , often indicated by adding ":1" to the value of the quotient (e.g.