Small white squares appear whiter than big white quares and small black squares appear blacker than the big black squares. There is of course no diffrence in the colors. Brightness of small squares appears to be enhanced by the background.

When squares of both colors are nearly equal we may observe Kitaoka's illusion or Kitaoka's waves (after Japanese artist Akiyoshi Kitaoka): the edges of the squares do not appear to form straight lines.

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