3D Display Technology-MASTER GUIDE

 3D DISPLAY TECHNOLOGY 

 3D display systems are capable of conveying a stereoscopic perception of real-world 3D depth to the viewer. The perception of 3D depth is produced by combining both of these 2D offset images in the brain. Although this method is widely used technique for "3D display”, it is effectively the presentation of dual 2D images. 3D is the capability to show 3D contents by referring to the use of dual 2D images as being "3D". A more recent advancement in display technology called holographic displays do not have this limitation. The term "3D display" fits accurately for holographic display technology. 

Stereoscopic technology is based on the principles of stereopsis and feeds a different image to the viewer's left and right eyes to produce the perception of 3D. This technology includes use of anaglyph images and polarized glasses. Most 3D TV work on this principle and give depth to the existing 2D images thus giving viewers the experience of realistic and natural three dimensional effects. 3D images can be produced by using 3D camera that uses two cameras installed in it which shoot the images as seen by left and right eye separately. These two images are delivered in agreed format after series of image processing activities to each eye, thus producing 3D image.

The most widely discussed forms of "3D" (stereoscopic) technology are:

1.  Active stereo 3D: This has been the standard solution for stereo 3D molecular visualization on the desktop which makes use of shutter glasses to produce the 3D effect for viewers and actively separate the images seen by the left and right eye.
2. Passive stereo 3D: In this technique, the effect of 3D is produced by applying special films to the screen, and polarized glasses are used to separate the images for the left and right eye respectively. It is used to deliver stereo 3D to audiences of more than a small group of people. 
3. Autostereoscopic 3D: This technique does not require use of glasses. This technology is prohibitively expensive at present and waits for large customer base.

 Stages of stereo 3D presentation 

Stereo 3D display technology has seen a great deal of innovation in the last few years. It is important to note that with the variety of display types available, the image pairs may be prepared in some format but the display handle and present them differently. Broadly, the stages of a stereo 3D presentation can be described by Figure 1.21.

The task carried out in each stage of the stereo 3D presentation is described below. 

1. Source: It is responsible for stereo 3D content creation or playback. In this stage left and right images ("image pairs") are generated. It may be done in two ways native stereo 3D generation or stereo 3D conversion. Native stereo 3D technique produces image pairs by an application (either 3D rendering, or video playback of Stereo 3D content). On the other hand stereo 3D conversion uses additional software, of stereo image pairs using a monoscopic source. It can deliver stereo image pairs for applications that are not written to natively support Stereo 3D. 
2. Preparation and transmission: This is responsible for preparing stereo 3D image pairs for display and relaying them to the display device. The prepared images are transmitted to that display over a display interface in a format that the display can interpret and use. Dual-link DVI, HDMI 1.4a and Display Port have the ability to transmit stereo images. Additionally, a synchronization signal for these images is also generated and transmitted. 
3. Presentation: The presentation of the prepared image pairs is the responsibility of the display device. This involves the actual display of left image and right image of the pair to the corresponding eyes, using stereo glasses. There are two main approaches — use of active, frame sequential, display with shutter glasses and passive (polarizing) display, and polarized glasses. First approach uses active frame sequential display with shutter glasses while second approach is to use passive (polarizing) display and polarized glasses. In the first approach, the display presents left and right eyes in sequence and shutter glasses are synchronized with that display. Polarizing glasses also known as wavelength filtering glasses may be created using dual display technology. In this technology, two displays present images with different polarization typically aligned with a half-mirror to permit the light from both displays to be presented together to the viewer's eyes. This results in full brightness and full resolution stereo to be presented to the user. Another more common is the low cost single display method. In this method, a polarizing filter is applied to the front glass of a display, cautiously aligned to rows or columns of pixels.

Active shutter technology (SG) 

It is the first mainstream method based on time division switching for delivering 3D content to desktop LCD monitor using shutter glasses (SG). The name "active" is relevant due to the active role of its glasses in the production of the 3D effect. This technology uses liquid crystal shutter glasses (also known as LC shutter glasses or active shutter glasses). These special shutter glasses together with certain type of 3D enabled display, graphics card, and software package helps to create the illusion of a three-dimensional object (from set of images). 

The eye glasses contains a liquid crystal layer which becomes dark when voltage is applied to them, being otherwise transparent. A special transmitter connected to the display controls these glasses by sending timing signals and makes glasses to alternately darken over one eye, and then the other. This is done in synchronization with the refresh rate of the screen. A technique called alternate-frame sequencing is used by the display to alternately display different perspectives for each eye, which achieves the desired effect of each eye able to see only the image intended for it. Effectively, each eye glass open and close at a very fast rate (typically 60 times per second) and alternate between the right and left eye glass thus allowing image being viewed to be seen by only one eye at a time. The synchronization of the glasses to the sequential left and right eye frames nowadays done through emitter that communicates to the glasses. NVIDIA and AMD offer 3D vision using SG technology, and Samsung, Sony, and Panasonic back the active shutter technology as their preferred method of delivering 3D to consumers.

Features of SG technology 

Some important features of SG technology include 

• High 120 Hz refresh rates: Overcomes the problems of flicker caused by the fading of pixels and provides true support of 120 Hz input frequencies. This in turn can allow 60 Hz per eye and a far higher frame rate, improved perceived motion on an LCD screen, and also help show smoother moving images.
• High resolution and "Full HD 3D": Active shutter methods are known to have "full HD 3D" feature and able to support 1080p resolution properly. In SG method, the full 1920 x 1080 resolution (of a 1080p image) is transmitted to each eye. 
•  Use of active shutter glasses: SG technology is reliant on active shutter glasses which are actively producing the 3D effect when in use. Active shutter glasses are more expensive than passive 3D glasses that are used in FPR methods described later. They are quite bulky and battery powered. Many early versions of the glasses work best in certain conditions with all nearby lights turned off and in darkened room conditions to view 3D contents. Often there are issues with compatibility of these glasses between vendors and between different screens. Figure 1 .22 shows Samsung's 3D active shutter glasses. 
•  Crosstalk issues: Due to the short interval between the shutter to open and close, there is a possibility of crosstalk. Crosstalk is overlapping of the image for one eye (of one side) with the image for other eye (of the other side) which is not supposed to be seen. To minimize this problem, a black image is inserted between the left and right images, or in many cases the backlight is temporarily turned off. 
•  Flicker and eye fatigue: A noticeable degree of flicker is introduced because the operation of active shutter glasses requires the lenses to be switched continually on and off in sync with the displays refresh rate. Due to high refresh rates (120 Hz), over time the flickering (not visible as such) can lead to eye fatigue or sometimes dizziness and headaches. This is one of the important reasons for manufacturers to move instead to passive 3D solutions. 
• Brightness: One of the known issues is that the active shutter glasses already have a tint to them and the perceived brightness of the image is reduced significantly when viewing contents. 

Polarized passive 3D technology 

The polarized passive 3D technology is more "true" 3D technique. In this technology, the 3D effect is actually produced by the screen or projected image and not by the eye glasses. Contrary to SG technology, the glasses are not active in creating the 3D content and instead handle the polarization of the image being shown. This gives the name "passive" technology typically used by cinemas to show modern 3D films. 

In projection system, such as that at a cinema, two images that are polarized in a different direction are projected onto the screen. The lenses of the glasses are polarized in opposite directions, with each lens matching the polarization of its corresponding left/right image. The left eye can only see the left image due to the fact that polarized lens covering the left eye is polarized to block the right image, while the right eye can only see the right image because the polarized lens covering the right eye is polarized to block the left image. On flatscreen TV, the addition of a special film is used which polarizes the image and splits it to what the left and right eye see when combined with the polarized glasses. Effectively the film filters the light to ensure that the correct eye views the correct left or right image. 

Passive 3D method for monitors and TV's by manufacturers like have come up with "Filmtype Patterned Retarder" (FPR) technology which are increasingly popular and widely used