3D Glasses 101

We've explained the 3D formats and rounded up 3D TVs and 3D Blu-ray players. So let's dive a little deeper in to 3D glasses and how they work.

Just like any emerging technology, there are a plethora of specifications and systems, few of which are directly compatible. The 3D Blu-ray spec and HDMI 1.4 are going a long way to unify, as are displays supporting multiple specs. But there’s still a lot to learn.

The bulk of modern home 3D technologies will rely on active shutter glasses. The glasses themselves all basically work the same way, using liquid crystal shutters to allow only one eye to see what’s on the screen at any given time.

Frame Progression Type

While they work the same, what they are allowing each eye to see can differ greatly. Here are some examples.

Interlacing - Alternating lines of resolution are drawn in sequence. Lines 1, 3, 5 ... are drawn while the right eye is exposed, then lines 2, 4, 6 ... are drawn as the left eye is exposed. Interlacing is one of the easiest methods in terms of hardware requirements, but limits resolution to half the display’s capability (since only half the image is displayed to each eye). Popular in older 3D gaming, it requires interlaced capable display such as a CRT monitor.

Page Flipping - Page flipping alternates the frame, left and right, in sync with the shutter of the glasses. This overcomes the resolution deficiencies of the interlacing method, but requires high refresh rates to minimize flicker and motion artifacts. The new 3D Blu-ray spec is based on a modified version of page flipping called frame stacking.

Checkerboard - Similar to interlacing, a checkerboard pattern is displayed in sync with the shutter of the glasses. The same resolution limits exist, but scan lines and other interlacing artifacts are minimized. This is the method used in "3D-Ready" DLP TVs offered by Mitsubishi and Samsung. An external adapter is required for use with 3D Blu-ray spec devices.

Sync Type

Since active shutter glasses require the shutter and display be in sync, they also require some sort of signal be sent to the glasses to keep them in sync. Current displays and gaming technologies use one of two methods:

Bluetooth - The active shutter glasses are paired with the display via Bluetooth RF frequency, similar to a wireless ear piece with your cellphone, but the only signals present are sent from the display to the glasses for sync of the shutters. Range can be limited, but in practice the range usually exceeds the likely viewing distance by a safe margin.

IR Emitter - Instead of radio frequencies, an IR emitter on or connected to the display emits an infrared signal that is detected by the glasses and syncs the shutter with the display. Range is greater than Bluetooth, but in rare instances, certain lighting conditions can interfere with the IR signal.