By Frederic Friedel

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Professor Richard Gregory in 2010, outside the original Café on St Michael’s Hill, where he described the illusion around forty years ago.
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An interesting feature displayed in the Café Wall illusion (and described in the Gregory/Heard paper) is the role the luminescence of the mortar lines plays. It needs to lie between the luminescence of the dark and light tiles. The image in the middle above works best, although they are all geometrically alike.
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Here is a larger version by Victoria Skye for you to play around with.

Perfect circles illusion

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Will you believe that these are two absolutely identical pictures placed next to each other?

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Frederic Alois Friedel, born in 1945, science journalist, co-founder of ChessBase, studied Philosophy and Linguistics at the University of Hamburg and Oxford.

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