Why Are 3D Glasses 3d?

3D or stereoscopic glasses give depth to an image.  We usually associate the glasses with films.  When we see a film on a screen, for example, it looks flat.  When a movie is filmed in 3D, the glasses are needed to make the images seem like they are right in front of us.

In the "real" world each of our eyes seen an image with a slightly different view.  The two images are brought together in the brain, and we see them in 3D (3 dimensions-height, width, and depth).  When something is filmed in 3D, two cameras are required to shoot an object with two different views.  That's why when a 3D film is viewed wihout the glasses, it looks fuzzy.  The lenses of 3D glasses, one red and  one blue, simply recreate the way humans see normally.  

When a 3D picture is shown, the scene is projected simultaneously from two diffrent angles in two different colors, blue and green or red and cyan.  The different colored lenses in the glasses filter the two images so that each eye sees only one image.  The brain puts the two images together, and voila, a 3 dimensional picture.