Active shutter 3D system
An active shutter 3D system (a.k.a. alternate frame sequencing, alternate image, AI, alternating field, field sequential or eclipse method) is a technique of displaying stereoscopic 3D images. It works by only presenting the image intended for the left eye while blocking the right eye's view, then presenting the right-eye image while blocking the left eye, and repeating this so rapidly that the interruptions do not interfere with the perceived fusion of the two images into a single 3D image.
Modern active shutter 3D systems generally use liquid crystal shutter glasses (also called "LC shutter glasses"[1] or "active shutter glasses"[2]). Each eye's glass contains a liquid crystal layer which has the property of becoming opaque when voltage is applied, being otherwise transparent. The glasses are controlled by a timing signal that allows the glasses to alternately block one eye, and then the other, in synchronization with the refresh rate of the screen. The timing synchronization to the video equipment may be achieved via a wired signal, or wirelessly by either an infrared or radio frequency (e.g. Bluetooth, DLP link) transmitter. Historic systems also used spinning discs, for example the Teleview system.
Active shutter 3D systems are used to present 3D films in some theaters, and they can be used to present 3D images on CRT, plasma, LCD, projectors and other types of video displays.
Video
Advantages and disadvantages
Advantages
- Unlike red/cyan color filter (anaglyph) 3D glasses, LC shutter glasses are color neutral, enabling 3D viewing in the full color spectrum, though the ColorCode anaglyph system does come very close to providing full color resolution.
- Unlike in a Polarized 3D system, where the (usually) horizontal spatial resolution is halved, the active shutter system can retain full resolution (1080p) for both the left and right images. Like any system, manufacturers of televisions may choose not to implement the full resolution for 3D playback but use halved vertical resolution (540p) instead.[3]
Disadvantages
- Flicker can be noticed except at very high refresh rates, as each eye is effectively receiving only half of the monitor's actual refresh rate. However, modern LC glasses generally work in higher refresh rates and eliminate this problem for most people.
- Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high-enough refresh rates to work with some LC shutter systems.[4] Many projectors, especially DLP-based ones, support 3D out of the box.
- LC shutter glasses are shutting out light half of the time; moreover, they are slightly dark even when letting light through, because they are polarized. This gives an effect similar to watching TV with sunglasses on, which causes a darker picture to be perceived by the viewer. However, this effect can produce a higher perceived display contrast when paired with LCDs because of the reduction in backlight bleed. Since the glasses also darken the background, contrast is enhanced when using a brighter image.
- When used with LCDs, extreme localized differences between the image to be displayed in one eye and the other may lead to crosstalk, due to LCD panels' pixels sometimes being unable to fully switch, for example from black to white, in the time that separates the left eye's image from the right one. Recent advancements in the panel's response time, however, has led to displays that rival or even surpass passive 3D systems.
- Frame rate has to be double that of a non-3D, anaglyph, or polarized 3D systems to get an equivalent result. All equipment in the chain has to be able to process frames at double rate; in essence this doubles the hardware requirements.
- Despite a progressive fall in prices, due to the intrinsic use of electronics, they remain more expensive than anaglyph and polarized 3D glasses.
- Because of their integrated electronics and batteries, early shutter glasses were heavy and expensive. However, design improvements have resulted in newer models that are cheaper, lightweight, rechargeable and able to be worn over prescription lenses.
