3D glasses work by using two sets of slightly offset images — one for each eye. In turn, our brain perceives those separate images as a single whole one, just like we see things naturally.^[1] Older anaglyph glasses — usually with red & cyan lenses — filter images for each eye by color. In turn, when the 3d movie is projected on the screen, two images are displayed — one in red, one in blue. However, it often distorts movie colors. Fortunately, newer polarized glasses don't have this drawback as they filter images by wavelength. They gained popularity after James Cameron's Avatar and became the best pick for 3D movies.