How do 3D Eyeglasses help to watch 3D films?

When we go for watching a 3D film in theatre, we always notice the print of film on the screen is blur. Then we wear a special type of eyeglass and get clear print with some 3D effects. What's the science behind that? Let's explore it!!
A three dimensional film is basically two polarised motion picture, having same linear polarisation but oriented differently, which are superimposed on each other. Hence, it is difficult to watch the film clearly and comfortably.

These special eyeglasses are linearly polarised eyeglasses which contains a pair of polarised filters. First one is oriented same as first picture and second one is oriented same as second picture. These filters pass the similarly polarised light through it and block the oppositely polarised light. Each side of glasses filters one of the two pictures and we get a perfect three dimensional effect in our vision.