Surely not. The A square is darker, much darker! Most people would put money on it. But they'd lose. Open it in Photoshop and inspect the pixel values. Or on the Mac open up the DigitalColor Meter application and take a peek .

Edward H Adelson explains it all in great depth in his paper Lightness Perception and Lightness Illusions. There are some great interactive illusions on the web site as well.

Tags: Optical Illusions, Interesting Stuff