Checker shadow illusion

Description

Verification

• Open the illusion in an image editing program and using the eyedropper tool to verify that the colors are the same.
• Right-click the image and select "View Image". Now zoom in to the image and hold a finger in front of your face, blocking out the connecting square. Since your finger is a different color and not merely a tone, your eyes will be able to compare A and B individually.
• Cut out a cardboard mask. By viewing patches of the squares without the surrounding context, you can remove the effect of the illusion. A piece of cardboard with two circles removed will work as a mask for a computer screen or for a printed piece of paper.
• Connect the squares with a rectangle of the same color, as seen in the figure to the right.
• Use a photometer.
• Print the image and cut out the squares. Cut out each square along the edges. Remove them. Hold them side by side.
• Isolate the squares. Without the surrounding context, the effect of the illusion is dispelled. This can be done by using the eyedropper tool in image editing programs, such as Gimp to sample the values of A & B, and to color in the newly adjacent rectangles using the paint bucket tool.