Mach band

A Mach band is an optical illusion, named after Ernst Mach. It is the region encircling a bright light which in visual perception appears lighter or darker than its surroundings, in a zone where the luminance increases or decreases rapidly.

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Although the physical brightness is constant over the distance from the ambient object, the observer perceives an "undershoot" and "overshoot" in brightness at what is physically a step edge. Thus, at a certain point, the observer perceives a slight decrease in brightness compared to the true physical value. After that point the observer undergoes a slight overshoot in brightness compared to the true physical value. The total effect is one of increased, local, perceived contrast at an edge in brightness.

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It is theorised that the Mach band may be responsible for moths' attraction to ambient objects.

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Optical illusion: An optical illusion is a type of illusion characterized by visually perceived images that are deceptive or misleading http://www.answers.com/topic/optical-illusion. Information gathered by the eye is interpreted by the brain to give the perception that something is present when it is not. There are ...

Ernst Mach: Ernst Mach (February 18, 1838 – February 19, 1916) was an Austrian-Czech physicist and philosopher and is the namesake for the "Mach number" and the optical illusion known as Mach bands....

Luminance: The word luminance, a synonym for luminosity, means emitting or reflecting light....

Mach band related Images and Photos (experimental)

Mach 5	Jazz Band	Rock Band	Jazz-Band
Jazz Band	Magic Band	Queen - Band	The Band c.1973
The Band c.1973	Band-In-A-Box	Mach 5 Cutout	Cantina Band