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Archives for October 2012

De schaakbord schaduw illusie

1 October 2012 by Gert Jan van 't Land 8 Comments

LEES DIT MET CHROME. Je gelooft je ogen niet:

The video you’re watching is a real-life demonstration of an optical illusion developed in 1995 by Edward Adelson, a professor in MIT’s Department of Brain and Cognitive Sciences. The Checker Shadow Illusion, as Adelson calls it, shows that our “visual system is not very good at being a physical light meter.” But more importantly, the optical illusion offers important insight into how our visual system tries to break down “image information into meaningful components, and thereby perceive the nature of the objects in view.” Adelson’s full explanation of the illusion and what it reveals appears below the jump (or here). H/T 3 Quarks Daily

 The visual system needs to determine the color of objects in the world. In this case the problem is to determine the gray shade of the checks on the floor. Just measuring the light coming from a surface (the luminance) is not enough: a cast shadow will dim a surface, so that a white surface in shadow may be reflecting less light than a black surface in full light. The visual system uses several tricks to determine where the shadows are and how to compensate for them, in order to determine the shade of gray “paint” that belongs to the surface.

The first trick is based on local contrast. In shadow or not, a check that is lighter than its neighboring checks is probably lighter than average, and vice versa. In the figure, the light check in shadow is surrounded by darker checks. Thus, even though the check is physically dark, it is light when compared to its neighbors. The dark checks outside the shadow, conversely, are surrounded by lighter checks, so they look dark by comparison.

A second trick is based on the fact that shadows often have soft edges, while paint boundaries (like the checks) often have sharp edges. The visual system tends to ignore gradual changes in light level, so that it can determine the color of the surfaces without being misled by shadows. In this figure, the shadow looks like a shadow, both because it is fuzzy and because the shadow casting object is visible.

The “paintness” of the checks is aided by the form of the “X-junctions” formed by 4 abutting checks. This type of junction is usually a signal that all the edges should be interpreted as changes in surface color rather than in terms of shadows or lighting.

As with many so-called illusions, this effect really demonstrates the success rather than the failure of the visual system. The visual system is not very good at being a physical light meter, but that is not its purpose. The important task is to break the image information down into meaningful components, and thereby perceive the nature of the objects in view.

Via: http://www.openculture.com/2011/08/mit_checker_shadow_illusion.html

Filed Under: Overig, Skeptische TV Tagged With: schaakbord illusie, video

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Recente reacties

  • Hans1263 on De linke weekendbijlage (24-2025)Benieuwd naar het resultaat. Vaak is de klokkeluider de kwaaie pier.
  • Renate1 on De linke weekendbijlage (24-2025)@ Hans Hier hebben we 2 psychologen die kennelijk vinden dat Trump psychisch gestoord is. https://www.youtube.com/watch?v=Ga3Ft15_-tA
  • Hans1263 on De linke weekendbijlage (24-2025)Ik weet het @ Renate. Maar er zal toch wel een Democraat zijn te vinden die proleet T. zo haat
  • Renate1 on De linke weekendbijlage (24-2025)@ Hans Ik denk dat psychologen en psychiaters vinden dat ze geen oordeel mogen uitspreken over mensen die ze niet
  • Hans1263 on De linke weekendbijlage (24-2025)Ik bedoelde psychiaters en psychologen. Zo moeilijk is een beoordeling toch niet, ook niet als je Trump niet zelf onder

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