Constructing Shades of Grey

In the figure on the left are various grey patches. You might be surprised to learn that two of these patches, corresponding to A and B in the figure on the right, are identical greys (i.e., a photometer would find them identical). However they appear to be very different greys. This is evidence that your Visual Intelligence constructs the greys that you perceive. This figure was devised by Ted Adelson.

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