Comment on Bizarre Illusions

Thu, 28 Jan 2010 00:35:30 GMT

I think the key for me in understanding this type of illusion (and the general phenomenon of colour constancy) was to realize that 'colour' in common usage ("this ball is blue") is perceived as a property of objects and we infer it indirectly based on light that reaches our retinas. That light also has a 'colour' (subtly different meaning) but it is not something we perceive directly because it is not very useful in itself.

This makes perfect sense when you think about it from an evolutionary perspective - we evolved to recognize invariant properties of objects in the world (possibly fruit in trees for primates) under widely varying lighting conditions. Directly perceiving the 'colour' (RGB) of light would not tell us anything very useful about invariant object properties. There is enough overlap between the two meanings of colour for them to be easily confused however and that is really the root of this particular illusion.

In computer graphics we commonly use the term 'material' to describe the set of properties of a surface that govern how it responds to incident light. This encompasses properties beyond simple colour ("shiny blue ball", "matte blue ball", "metallic blue ball"). I don't know if that usage is well understood outside of the computer graphics field however.

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