Active Shutter vs. Passive Glasses
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Active Shutter 3D Glasses

Active shutter glasses are the standard for Blu-ray 3D and are currently a very popular choice among consumer electronics giants who are investing in 3D display technology. The primary reason for this is that this technology requires a very minimal modification to current HDTV displays and as a result it is much easier to develop and perfect. The individual eye pieces of these glasses incorporate liquid crystals and a polarization filter so that when a voltage is applied, the glass turns dark and prevents light from transmitting through. Thus the left and right eye glass can be shuttered alternatively in this manner and this shuttering effect is synced with the refresh rate of the display. The 3D TV displays a frame for the left and right eye alternatively and the sync with the active shutter glass ensures that each eye only ever views the image it is meant to see. As is probably evident, because of the way these displays work, the effective refresh rate of the TV is halved. This is why 3D Ready TVs have to have a minimum refresh rate of 120 Hz (meaning 60 frames per second for each eye).

Advantages of Active Shutter Glass Technology

  • Inexpensive screens. This is because this technology only needs a refresh rate enhancement for current LCD and Plasma TVs, something that isn’t too hard or expensive to do. In addition a syncing unit will be required to sync the TV to the active shutter glasses
  • Highest quality 3D image quality. The technology allows full frame 1080p images to be displayed for each eye, rather than displaying half-resolution images per eye that are decoded from a single frmae containing both left and right-eye views.
  • Backward compatible with some of the high-end 3D capable TVs that were sold in 2008 and 2009
  • Displays are based on very mature LCD, DLP and Plasma technology. Which means that most of the quirks are already ironed out and prices shouldn’t be prohibitive.

Disadvantages of Active Shutter glasses

  • Glasses are battery powered. This is one major drawback that is not particularly easy to alleviate. Due to the nature of the technology the glasses need to apply a potential to “shutter” the glasses. It also needs additional power to communicate and sync with the TV.
  • Glasses are expensive. While the 3D displays using this technology will be inexpensive themselves, the glasses will be more expensive than their passive counterparts due to their complexity. This means that it might be a bit prohibitive to own many active shutter glasses for when you have friends come over to watch a 3D movie. However, it is most likely that they will be well subsidized by the display manufacturers in an effort to encourage widespread 3D TV adoption.

Passive Polarized 3D Glasses

There has been resurgence in Passive 3D Glasses technology in the past decade due to technological progress that has enabled Digital projectors such as those used by RealD and IMAX 3D to display commercial movies at movie theaters in true 3D. These systems rely on exploiting a property of light called polarization which relies on discriminating between two images projected on the same screen by 2 separate projectors based on the polarization of the light used to project the image. When light of one polarization encounters an eye-piece that is polarized in the opposite direction, it cannot pass through. On the other hand, if both the lens and the light have the same polarization, then the light passes through the lens unimpeded. Thus, each eye piece has the opposite polarization and the image projected on the screen consists of two images, each possessing a different polarization and perspective, meant for one eye. In this manner, a separate image is delivered to each eye.

In commercial 3D projectors used in theaters, the projector technology relies on Circularly polarized light which works in a similar manner but also allows the viewer to tilt his or her head without degrading the image quality. These projectors also save on costs since they can alternatively generate right circularly polarized and left circularly polarized images in rapid succession without the need for two independent projectors.

Passive 3D Plasma and LCD screens have a polarised filter in front of the screen that gives opposite polarisation to alternate lines: Even-numbered lines are polarised in one direction, odd-numbered lines in the other. The the polarized filter glasses cause the left eye to only see the even-numbered lines, for example, and the right eye to only sees odd-numbered lines.

Advantages of Passive Polarized 3D Glasses

  • Passive 3d Glasses are extremely cheap. You can easily stock up on them if you are planning to have a big Super Bowl party where you want to show off your fancy 3D TV. Additionally, there is a good chance that the glasses you kept from when you went to the theater will actually work for your passive polarized 3D display.

Disadvantages of Passive Polarized 3D Glasses

  • Half-resolution image quality. Each eye sees only half of the vertical resolution of a 2D picture because both left eye and right eye images are contained in the same frame.