Presentation Transcript
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