Most of you probably already know this. But this is how 3D works without glasses.
Two images (Right image and Left Image) with different perspectives are interlaced onto a screen simultaneouly. A filter known as Parallax Barrier, has a series of precision slits that allows each eye to see a different set of pixels for each perspective. Our brain processes these images into one image to produce the illusion of 3 Dimensional space.
Parallax Barrier 3D Technology - 3D Without Glasses
Parallax barrier - Wikipedia, the free encyclopedia
I found the above information on the web.