Do not trust your eyes again!!!!!

The squares marked A and B are the same shade of gray.,,,,Yes true and i can prove it to you..how??four ways :
1) Try putting the image in Photoshop.Using the eyedropper tool you can determine that the RGB values of the grays in both square A and square B are 120-120-120.

2) 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 computerscreen or for a printed piece of paper.

3) Print the image and cut out the sqaures.This is another way to isolate the patches form their surrounding context. Cut out each square along the edges. Remove them. Hold them side by side. Please note that some printers, especially laser printers, have "enhancement" processing that increases the contrast of edges. This can cause the printed squares to have slightly different values of gray.

4) Get a photometer.
finally do this..

The original image plus two stripes.By joining the squares marked A and Bwith two vertical stripes of the sameshade of gray, it becomes apparentthat both squares are the same.