Does this image appear three dimensional to you? Do you think that there is a sphere lying over the top of a checker board? If you think that, believe us, it is just your perception. This image is perfectly two dimensional only. Even the lines are perfectly parallel. There is no real bulging and it is just a circle of pattern. The circle appears to be as a sphere just because of the pattern that has been used inside it in comparison with the pattern that has been used outside i.e. black and white checkers.