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HSPA(High Speed Packet Access) 1.1 ABSTRACT
The stereoscopic display technology has become a main research issue in recent years because of its unique human-computer interaction. Three dimensional (3D) displays, mostly stereoscopic, are becoming part of our life. There are several technologies to achieve the 3D effects. Stereoscopic display technology is used to create a illusion of depth to human eyes in the photo or video which is being watched. Nowadays mostof the devices come with 3D display capability, and all this devices are using stereoscopic display technology to give 3D effect.
This report analyzes the principle of stereoscopic display and then briefly introduces the different types of available stereoscopic display technologies and the devices used in this technology meanwhile it also talks about the principles, applications, advantages and disadvantages of stereoscopic display technologies, and at last talks about stereo window concept in this technology and what is next following this technology in future.
1.2INTRODUCTIONStereoscopy is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. Most stereoscopic methods present two offset images separately to the left and right eye of the viewer. These two-dimensional images are then combined in the brain to give the perception of 3D depth. This technique is distinguished from 3D displays that display an image in three full dimensions, allowing the observer to increase information about the 3-dimensional objects being displayed by head and eye movements.Stereoscopy creates the illusion of three-dimensional depth from given two-dimensional images. Human vision, including the perception of depth, is a complex process which only begins with the acquisition of visual information taken in through the eyes; much processing ensues within the brain, as it strives to make intelligent and meaningful sense of the raw information provided. One of the very important visual functions that occur within the brain as it interprets what the eyes see is that of assessing the relative distances of various objects from the viewer, and the depth dimension of those same perceived objects.
2.1NEED FOR STEREOSCOPYInitially in early 19th century, there were no television box for watching videos, and people used to perform skits in theatre and as time went by theatres came into picture where screen was used to project the movies which were recorded using a bulky video recorder, and then slowly as time went on more research and more inventions resulted in making a smaller television set for watching movies in our home comfortably and by the end of 19th century , television set was so affordable that everyone had one television set at home , and now people got bored of it slowly and they wanted something new , something more exciting and something more entertaining than plain old 2D supporting Television box.This led to beginning of research on enabling a totally new kind of experience while watching the video, a feeling of being inside the movie or giving depth to the images and videos that are seen in the movies. This gave rise to invention Stereoscopic display technology, which helps in giving 3D illusion to the movie or images that people are watching.
2.2WHAT IS STEREOSCOPY?Stereoscopy also called as 3D imaging is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek word stereos, meaning "firm, solid", and skopeo meaning "to look, to see". Any stereoscopic image is called stereogram. And any devices used for stereoscopy are called stereoscope.One of the very important visual functions that occur within the brain as it interprets what the eyes see is that of assessing the relative distances of various objects from the viewer, and the depth dimension of those same perceived objects. The brain makes use of a number of cues to determine relative distances and depth in a perceived scene, including Stereopsis, Accommodation of the eye, Overlapping of one object by another Subtended visual angle of an object of known size, Linear perspective, Vertical position, Haze, and Change in size of textured pattern detail Fig 2.1: An early stereoscopic card for viewing a scene from natureStereoscopic display technology uses all the above mentioned cues to trick the mind and create an illusion of depth by giving two seperate images to two eyes. Fig 2.1 shows the old picture used for stereoscopic view in early 19th century.
Although the term "3D" is ubiquitously used, it is also important to note that the presentation of dual 2D images is distinctly different from displaying an image in three full dimensions. The most notable difference is that, in the case of "3D" displays, the observer's head and eye movement will not increase information about the 3-dimensional objects being displayed. Holographic displays or volumetric display are examples of displays that do not have this limitation. Similar to the technology of sound reproduction, in which it is not possible to recreate a full 3-dimensional sound field merely with two stereophonic speakers, it is likewise an overstatement of capability to refer to dual 2D images as being "3D". The accurate term "stereoscopic" is more cumbersome than the common misnomer "3D", which has been entrenched after many decades of unquestioned misuse. Although most stereoscopic displays do not qualify as real 3D display, all real 3D displays are also stereoscopic displays because they meet the lower criteria as well.Traditional stereoscopic photography consists of creating a 3D illusion starting from a pair of 2D images, a stereogram. The easiest way to enhance depth perception in the brain is to provide the eyes of the viewer with two different images, representing two perspectives of the same object, with a minor deviation equal or nearly equal to the perspectives that both eyes naturally receive in binocular vision.
2.3TYPES OF STEREOSCOPIC DISPLAY TECHNOLOGY
Stereoscopic Display technology can be divided into two groups1. Manual Stereoscopic Display Technology2. Automatic Stereoscopic Display Technology
Manual Stereoscopic Display Technology is the most widely used stereoscopic display technology in present days. In this technology viewers need to wear a glass in order to enjoy the stereoscopic display. The glasses can be either active or passive devices. Active devices uses electronic device to power the glasses and to synchronise the glass shutters. Example for this active device is Shutter Glass Stereoscope. Passive devices are those which doesnt need any kind of electronic device in the glass, this are the most famous and widely used devices in stereoscopic display technology. Examples for passive devices are anaglyph glasses and polarization glasses.
Automatic Stereoscopic Display Technology is the latest innovation in stereoscopic display technology in recent times and still not yet developed to its full capacity. This technology does not need the viewer to use any kind of glasses while watching the movie or image.People can get the Depth Illusion with the bare eyes. Nintendo 3DS is the example of this technology.
We need to understand how human eye analyses depth in order to understand the principle of stereoscopic display technology. When we watch an object with one eyed covered and then watch the same object with other eye closed this time and we see two different images.This is ofcourse because our eyes are a few inches apart; this is called the interocular distance and it varies from person to person. We should also note that when we look at something close, objects appear in double in the background. Its because we are actually rotating our eyes so they both point directly at what we are focusing on. This is called convergence, and it creates a sort of X, the center of the X being whats being focused on.
Fig 2.2: Formation of convergence X by eye
So the objects at the center of the X are aligned at the same points on our respective retinas, but because of the interocular, that means that things in front and behind of that X are going to hit different points on those retinas resulting in a double image.
Once the two images have been presented to our retinas, they pass back through the optic nerve to various visual systems, where an incredibly robust real-time analysis of the raw data is performed by several areas of the brain at once. Some areas look for straight lines, some for motion, some perform shortcut operations based on experience and tell us that yes indeed, the person did go behind that wall, they did not disappear into the wall, and that sort of thing. Eventually (within perhaps 20 milliseconds) all this information filters up into our consciousness and we are aware of color, depth, movement, patterns, and distinct objects within our field of view, informed mainly by the differences between the images hitting each of our retinas. Its important to note that vision is a learned process, and these areas in our visual cortex are programmed by experience as much as by anatomy and, for lack of instinct.
Fig 2.3: Picture describing how the image are sent to brain from retina
To understand how Stereoscopic Display Technology works we need to understand the above mentioned concepts, which are native 3D acquisition tools.
Stereoscopic Display technology use those concepts to create the illusion to the brain, before we used to focus on one plan 2D image and hence we could only get the depth or distance between that image and eyes and not the depth of the objects in the image , but now we display two different images to both the eyes of the same scene which tricks the brain as if we are seeing the real live view of the video and hence we are able the get the depth in the image or video that we are watching.
Thats the most simple principle of this technology that is it creates the illusion of depth by presenting a different image to each eye. And thats something that all 3D displays have in common, no matter what. But how best to display it? Everyone differs in their opinions. standards were even developed that encode a 3D stream similarly to normal stream, except with totally separate left and right eye images baked right in. There are variations, of course, but its a surprisingly practical approach they agreed on.
3.2ENCODING METHODSOne way to distribute the 3D content is to deliver left and right views independently. However, this is not much of an encoding, quite wasteful in terms of bandwidth, packaging, and may be problematic to keep the two views correctly synchronized.Hence separate encoding methods had to be used inorder to distribute the 3D content
Presently there are 4 types of encoding methods for 3D content that are being used
1. Spatial Compression2. Temporal Interleaving3. 2D+ some form of Metadata4. Colour Shifting
This is useful when trying to deliver a 3D signal over the existing HD video infrastructure. It is also referred as frame compatible as it squeezes the left and the right image intoone HD frame. In order to do so it employs some kind of pixel sub sampling, so the downside is the loss in resolution. There are two aspects of this approach that need to be considered: the spatial sub-sampling and the frame packaging.The proposed spatial sub-sampling schemes are: taking alternate lines, taking alternate columns or sampling diagonally using a quincunx filter. After the sampling the images are repackaged in side-by-side or over/under format. The quincunx sampling is used and repackaged for transmission because its format is not efficient for direct compression. The quincunx signal can be used directly in HD interfaces that deal with the co-called checkerboard pattern and this is the signal format of choice for DLP displays.
TEMPORAL INTERLEAVINGThis method presents sequentially left and right images as full resolution frames. Therefore it requires doubling the frame rate and therefore doubling the bandwidth required for a normal 2D HD signal. Compression can use prediction between left and right views, but this tends to be no better than the normal temporal prediction. So the main saving is the reduction of the number of I frames.
2D + SOME FORM OF META DETAThe idea with this compression technique is to transmit a 2D signal and then some information that allows the reconstruction of a second 2D signal. This would be compatiblewith existing 2D displays, it may save bandwidth and it is included in MPEG. The most popular types of data suggested in order to supplement the 2D are a depth map (2D + depth); an optimized disparity map indicated as Delta (2D + D); a set of depth, occlusion and transparency maps (2D + DOT).Other suggestions include supporting multiple view coding as a way to future-proof the encoding standards to the possible adoption of auto stereoscopic and holographic displays.
COLOUR SHIFTINGColour shifting, associated with the anaglyph technique, uses red/green or red/cyan or some other two colour pairing. It is compatible with 2D displays, offers full resolution and glasses are inexpensive, but it is mainly a legacy technology.
4.1STEREOSCOPE DEVICESA stereoscope is a device for viewing stereographic displays, which are displays that contain two separate images that are printed side by side to create the illusion of a three-dimensional image. There are two types of Stereoscope Devices1. ACTIVE DEVICES2. PASSIVE DEVICES
Active devices are those devices which need an small electronic component on the glass which powers the glass system and also helps in synchronizing the signal. These devices are mostly used in theatres. Example of this type of device is shutter glass system
Passive devices are those devices which need no electronic help and dont need any power to run the glass system and there are no synchronizing of signals involved. This devices are used mostly in home entertainment systems because they are cheaper then the active devices and maintenance is also less. Example for this are Polarization system, Interference Filter system ,Chroma depth System and colour anaglyph system.
4.2.1SHUTTER SYSTEMSThis is the current method of choice for most 3D entertainment companies. The media is displayed at a high framerate, and the glasses rapidly switch between black and clear using a pair of low-latency transparent LCD screens. In this way, one eye sees nothing (for as little as a hundredth of a second or so) while the other sees its correct image, and a few microseconds later, the situation is reversed: the opposite eyes image is displayed and the LCDs have switched. The benefit is that each eye is getting the full image whenever its getting anything (unless theyre cheating and doing it via interlaced field switching).
Fig 4.1: Active Shutter System
There are number of objections to this technology like different company glasses vary in their performance , no single standard and the technology is still being improved, the glasses are costlier compared to other passive devices and maintenance cost is also very high and position and tilt can affect the image 3D depth.
4.3PASSIVE DEVICE4.3.1POLARIZATION SYSTEMSTo present a stereoscopic picture, two images are projected superimposed onto the same screen through different polarizing filters. The viewer wears eyeglasses which also contain a pair of polarizing filters oriented differently (clockwise/counterclockwise with circular polarization or at 90 degree angles, usually 45 and 135 degrees, with linear polarization). As each filter passes only that light which is similarly polarized and blocks the light polarized differently, each eye sees a different image. This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives. Additionally, since both lenses have the same color, people with one dominant eye (amblyopia), where one eye is used more, are able to see the 3D effect, previously negated by the separation of the two colors.
Fig 4.2 Polarized SystemsCircular polarization has an advantage over linear polarization, in that the viewer does not need to have their head upright and aligned with the screen for the polarization to work properly.
4.3PASSIVE DEVICE4.3.2COLOR ANAGLYPH SYSTEM
In an anaglyph, the two images are superimposed in an additive light setting through two filters, one red and one cyan. In a subtractive light setting, the two images are printed in the same complementary colors on white paper. Glasses with colored filters in each eye separate the appropriate images by canceling the filter color out and rendering the complementary color black. A compensating technique, commonly known as Anachrome, uses a slightly more transparent cyan filter in the patented glasses associated with the technique. Process reconfigures the typical anaglyph image to have less parallax.
Fig 4.2: Red-Cyan Anaglyph System
4.3.3INTERFERENCE FILTER SYSTEM This technique uses specific wavelengths of red, green, and blue for the right eye, and different wavelengths of red, green, and blue for the left eye. Eyeglasses which filter out the very specific wavelengths allow the wearer to see a full color 3D image. Special interference filters (dichromatic filters) in the glasses and in the projector form the main item of technology and have given the system this name. It is also known as spectral comb filtering or wavelength multiplex visualization.This technology eliminates the expensive silver screens required for polarized systems such as RealD, which is the most common 3D display system in theaters. It does, however, require much more expensive glasses than the polarized systems. Dolby 3D uses this principle.
Fig 4.3: Interference Filter System
4.3PASSIVE DEVICE4.3.4CHROMA DEPTH SYSTEMChromadepth is a patented system from the company Chromatek that produces a stereoscopic effect based upon differences in the diffraction of color through a special prism-like holographic film fitted into glasses. Chromadepth glasses purposely exacerbate chromatic aberration and give the illusion of colors taking up different positions in space, with red being in front, and blue being in back. This works particularly well with the sky, sea or grass as a background, and redder objects in the foreground.
Fig 4.4:A sample image used to demonstrate Chroma Depth system and the glass used for it
Any media piece can be given a 3D effect as long as the color spectrum is put into use with the foreground being in red, and the background in blue. From front to back the scheme follows the visible light spectrum, from red to orange, yellow, green and blue. As a result, ChromaDepth works best with artificially produced or enhanced pictures, since the color indicates the depth.
4.4AUTOSTEREOSCOPYAutostereoscopy is any method of displaying stereoscopic images (adding binocular perception of 3D depth) without the use of special headgear or glasses on the part of the viewer. Because headgear is not required, it is also called "glasses-free 3D" or "glassesless 3D". There are two broad approaches currently used to accommodate motion parallax and wider viewing angles: eye-tracking, and multiple views so that the display does not need to sense where the viewers' eyes are located. Examples of autostereoscopic displays technology include lenticular lens, parallax barrier, volumetric display, holographic and light field displays and Nintendo 3DS.
Fig 4.5 NINTENDO 3DS
4.5STEREO WINDOWFor any branch of stereoscopy the concept of the stereo window is important. If a scene is viewed through a window the entire scene would normally be behind the window, if the scene is distant, it would be some distance behind the window, if it is nearby, it would appear to be just beyond the window.To truly understand the concept of window adjustment it is necessary to understand where the stereo window itself is. In the case of projected stereo, including "3D" movies, the window would be the surface of the screen. With printed material the window is at the surface of the paper. When stereo images are seen by looking into a viewer the window is at the position of the frame. In the case of Virtual Reality the window seems to disappear as the scene becomes truly immersive.The entire scene can be moved backwards or forwards in depth, relative to the stereo window, by horizontally sliding the left and right eye views relative to each other. Moving either or both images away from the centre will bring the whole scene away from the viewer, whereas moving either or both images toward the centre will move the whole scene toward the viewer. Any objects in the scene that have no horizontal offset, will appear at the same depth as the stereo window.Considerations in deciding where to place the scene relative to the window involves deciding where individual objects are placed relative to the window. It would be normal for the frame of an actual window to partly overlap or "cut off" an object that is behind the window. Thus an object behind the stereo window might be partly cut off by the frame or side of the stereo window. So the stereo window is often adjusted to place objects cut off by window behind the window. If an object, or part of an object, is not cut off by the window then it could be placed in front of it and the stereo window may be adjusted with this in mind. This effect is how swords, bugs, flashlights, etc. often seem to "come off the screen" in 3D movies.
Enhances cinema experience. Cheap and lightweight 3D glasses that are affordable. A very simple system and quite easy to set up.
Viewers need to be in the ideal watching zone else they wont be able to see the 3D effect at its best. Viewers need to use glasses in order to see the 3D effect Stereoscopic content can in some cases cause varying degrees of eye-strain to some viewers, especially after watching for long periods of time. For standard Cable TV broadcasts, it is not possible to achieve 1080i High Definition for 3D content using the existing cable TV standards. Instead, 3D content is broadcast in a lower resolution format 3D TVs and 3D movies are expensive then watching normal 2D counterparts.
5.2WHATs NEXT ?Now -a-days more amount of research is going on how to get the effect of stereoscopic effect without uses of glasses that is Auto Stereoscopy field.Focus is put more on REAL 3D display where instead of illusion real 3D images and videos are displayed.
Many new technologies have been discovered and are under developing modeTwo of the most famous such technologies are1. Holographic Display2. Volumetric Display
Holographic display is a type of display technology that has the ability to provide all four eye mechanisms : binocular disparity, motion parallax, accommodation and convergence.
(a)Holographic Display (b)Volumetric Displays Fig5.1 Volumetric displays use some physical mechanism to display points of light within a volume. Such displays use voxels instead of pixels. Volumetric displays include multiplanar displays, which have multiple display planes stacked up, and rotating panel displays, where a rotating panel sweeps out a volume.
Stereoscopic 3D viewing provides greater immersion into a movie.
Stereoscopy is widely used technology for almost 90% of the 3D display systems. Devices are getting more improved and 3D stereo displays are (still) too expensive and (still) carry too many limitations to be of interest to the broader PC market. and hence focus is made on making the devices as cheap as possible so that every individual can afford it for day to day use in home and completely replace the older plain 2D Television boxes .
Now the research is more towards the Auto stereoscopic mode where 3D display is achieved without the glasses. But one thing is sure that no matter how perfected, stereo 3D will never be confused with a Real Environment.Of course, the development of 3D stereo technology is moving ahead. X3D has already announced a stereoscopic 17" TFT display for PC gamers that should cost somewhere around $1000.Using the software published by More3D, practically any 3D software can be displayed in 3D stereo. NVIDIA is also continuing the development and support of its consumer 3D stereo drivers.
 http://www.stereoscopy.com/ http://techcrunch.com/2010/06/19/a-guide-to-3d-display-technology-its-principles-methods-and-dangers/
 Recent development in stereoscopic display technology published in Communication Technology and Application (ICCTA 2011), IET International Conference by Lina Zhao,Fei Wang , Wei Liu
 Wang Dong-cui, Wang Hui-nan. About Stereoscopic Vision and True 3D Volumetric Display Technology[J].Advanced Display,2009(9]
 http://en.wikipedia.org/wiki/Stereoscopy http://en.wikipedia.org/wiki/Stereo_display Er Dong. Brief Discussion on three-dimensional display technology[J].Satellite TV & IP Multimedia, 2009(11]
Department of Electronics and Communication, PESIT-BSC