Is Colour an Illusion

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Is Colour an Illusion? Some contrast effects and the problem of constancy: Is Colour an Illusion? Some contrast effects and the problem of constancy Harald Arnkil Lecturer, Colour Studies, School of Visual Culture MediaLab, 25.10.2006 harald.arnkil@uiah.fi


Slide2: ”…the brain has to extract information about the essential, non-changing, apects of the visual world from the ever-changing information that is reachig it.” Semir Zeki, Inner Vision - An Exploration of Art and the Brain, 2003


Slide14: Is colour constancy a higher cognitive processes? But …even goldfish are found to have it!


Slide16: B) Reflectance image A) Illuminance image C) Luminance image The problem: How does the brain determine B from C?


Slide25: The Benary effect White’s illusion De Valois & De Valois


Slide30: Cornsweet – Craik – O’Brien effect


Slide31: From Edward H. Adelson: (a) The local ambiguity of edges. (b) A variety of junctions. Variations of the Craick – Cornsweet – O’Brien illusion


Slide36: Is the small chequer-board in shadow or are its lightest squares of medium grey reflectance?


Slide37: The significance of edges: shadow and penumbra


Slide38: How to separate brightness and lightness? The brain uses subtle visual clues to determine real surface lightness = reflectance of surface that is independent of illumination changes


Slide49: Barton L. Anderson & Jonathan Winawer