Stereoscopy (794220)
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Moscow State University Department of Computational Mathematics and Cybernetics.
Stereoscopy.
Kuznetsov N.
Group 213.
Moscow, 2010
Introduction
At first, I’d like to say, why I’ve chosen this subject for my abstact. Such a topic is quite popular nowadays and something like “Now in 3D” makes people to be interested in it. The most daily and common usage of stereoscopy is 3D-cinema, but points of how does it work and other aspects of stereoscopy are unknown, so I’ll try to retell you some information about it that I found.
Concept of Stereoscopy
Stereoscopy (also called stereoscopic or 3-D imaging) is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image.
Human vision uses several cues to determine relative depths in a perceived scene. Some of these cues are:
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Stereopsis (process in visual perception leading to the sensation of depth from the two slightly different projections of the world onto the retinas of the two eyes.)
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Accommodation of the eyeball (eyeball focus)
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Occlusion of one object by another
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Linear perspective (convergence of parallel edges)
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Vertical position (objects higher in the scene generally tend to be perceived as further away)
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Change in size of textured pattern detail
All the above cues, with the exception of the first two, are present in traditional two-dimensional images such as paintings, photographs, and television. Stereoscopy is the enhancement of the illusion of depth in a photograph, movie, or other two-dimensional image by presenting a slightly different image to each eye, and thereby adding the first of these cues (stereopsis) as well. It is important to note that the second cue is still not satisfied and therefore the illusion of depth is incomplete.
Many 3D displays use this method to convey images. It was first invented by Sir Charles Wheatstone in 1838. Stereoscopy is used in photogrammetry and also for entertainment through the production of stereograms.
Traditional stereoscopic photography consists of creating a 3-D illusion starting from a pair of 2-D images. 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 exactly equal to the perspectives that both eyes naturally receive in binocular vision. If eyestrain and distortion are to be avoided, each of the two 2-D images preferably should be presented to each eye of the viewer so that any object at infinite distance seen by the viewer should be perceived by that eye while it is oriented straight ahead, the viewer's eyes being neither crossed nor diverging. When the picture contains no object at infinite distance, such as a horizon or a cloud, the pictures should be spaced correspondingly closer together.
Different Approaches to Stereoscopy
The principle of stereoscopic vision is simple but hard to implement on the technical level. It is only necessary to show each eye a different picture as if the eyes were looking at the object from different points of view. The rest will be constructed and calculated by the human brain.
However, it is not so simple to implement this idea. There are currently a number of various ways to show the left and right eyes different pictures.
As opposed to audio equipment, you will not achieve a stereoscopic effect if you place two monitors in front of you. The eyes both normally focus in one point of the real space, so it is hard to look at the left and right monitors with your left and right eye, respectively. Well, you can force your eyes to focus in some point of space so that the images displayed by the monitors coincided, but this method requires training and will not work at all for some people. Moreover, it strains the eyes and thus can only be used for viewing special stereoscopic pictures. Although there are even special glasses offered for making such stereoscopic viewing easier, the method is not appealing at all. Besides, it requires as many as two monitors.
It would be logical, however, to just place two displays in front of the eyes. This is the principle that virtual reality helmets are based on. A VR-helmet includes massive glasses with small screens instead of lenses – one screen for each eye. An optical system is mounted in front of the screens to visually move the image away from the eyes – the user does not have to learn to focus his sight on the top of his own nose.
This system is ideal in separating the left- and right-eye frames because the two screens are absolutely independent from each other but such VR eyeglasses are very complex technically. The tiny screen has to have a good resolution (because the eye perceives it as a large screen viewed from a distance of 2-3 meters, so image graininess is quite conspicuous) while the electronics must be compact and light. Otherwise, the user’s neck will hurt under the load after watching a 2-hour movie or the glasses will slip down from his head under their own weight. As a result, VR glasses are expensive. You won’t even get a resolution of 640x480 for $200. And a pair of 1024x768 or higher VR-glasses will cost you a few thousand dollars.
The third and far more popular method of stereoscopy is in the use of anaglyphic glasses whose lenses are color filters – red and blue, usually. An image prepared for such glasses seems to double without them. But in the glasses each eye will see its particular picture because the red lens does not pass blue light and the blue lens does not pass red light. This is enough for the brain to construct a true 3D image.
The good point of the anaglyphic technology is in the use of one display for showing both pictures, in the rather simple preprocessing of visual content, and in the low price of the glasses. Made from a piece of cardboard and a couple of celluloid light filters, the glasses are cheap and can be even included with a cinema ticket or DVD disc without affecting the total price much. This made the anaglyphic technology widely popular in cinema houses that show 3D movies.
Of course, color accuracy suffers through the color separation of the left and right frames. Anaglyphic glasses cannot produce saturated colors because one eye does not see blue while the other eye, red. And both eyes do not see green well. Moreover, diopter correction of one of the lenses is necessary for looking at a monitor. Otherwise, the left and right eyes will see the picture in different color and focus somewhat differently, reducing the sharpness of the image. To sum up, this technology is simple but cannot reach perfection.
Polarizing glasses is yet another image separation method. Human eyes are not sensitive to light polarization, so if one and the same display device is used to simultaneously show pictures for the left and right eyes with different polarization and if you wear glasses with differently oriented polarizers instead of lenses, your eyes won’t notice anything wrong, but will see each its own picture. Polarizers are rather cheap, so the glasses are about as cheap as anaglyphic glasses but do not affect color reproduction.
It is rather easy to produce visual content for such glasses in a cinema house. You take two projectors working simultaneously with polarizers in front of each. And there is a metallized screen that does not change the polarization of the reflected light. One projector is displaying a film with the visual content for the left eye and the other projector, for the right eye. The visitors put on the provided eyeglasses and watch a 3D movie. This is the technology employed at IMAX movie theaters.
It is, however, problematic to use this technology at home because one projector is already quite a costly thing.
Zalman is offering Trimon series monitors that have a special film over the screen that makes the odd and even-numbered lines of the screen have different polarization. As a result, if you put on polarizing glasses, your left eye will see some lines while your right eye will see the other lines. Then, it is only necessary to produce two interleaved pictures and show them simultaneously in order to produce the stereoscopic effect.
The highs of this technology are obvious: cheap glasses (which means you can buy a few pairs to watch movies with all your family), normal color reproduction, reasonable price of the whole system, and the opportunity to use the same monitor for everyday work. Alas, Zalman did not manage to make its Trimon suitable for the latter application. When in 2D mode the Trimon is an ordinary 1680x1050 monitor but the additional polarizing film is quite visible: the screen seems to be crossed with thin horizontal lines, which doesn’t look nice. Moreover, the monitor works at only half the vertical resolution in 3D mode (each eye sees a 1680x525 picture) while the viewing angles are rather limited.
And most importantly, this technology is Zalman’s property. So far you can only choose one of two available models differing in screen size. And the Trimon series monitors are far from perfect in terms of design and setup, which is quite a serious drawback, too.
The developers from iZ3D offer another version of this technology: a monitor with two sandwich-like matrices. The bottom matrix produces the combined picture for both left and right eyes while the top, simpler, matrix rotates the polarization plane, to give each eye the necessary share of light. The iZ3D monitor must be used with a pair of cheap passive glasses with polarizers.
As opposed to Zalman’s Trimon, the iZ3D works at full 1680x1050 resolution in each mode. It does not have horizontal lines on the screen and its viewing angles are considerably wider. Therefore I thought it a more promising technology than the Trimon. However, the iZ3D has drawbacks of its own. The manufacturing cost of such monitors is high due to the double matrix, and the second matrix worsens image sharpness in 2D mode a little. And most importantly, this technology is only supported by two models manufactured by one firm, making your shopping choice very limited.
But even back at the end of the last century there was a technology that could produce a high-quality stereoscopic picture on almost any monitor. Its most well-known implementation was the 3D Revelator eyeglasses from ELSA that had liquid-crystal shutters instead of lenses. The shutters could change their opaqueness, getting darker or lighter as commanded.
The point of the technology is simple enough. The monitor is working with a refresh rate of 120Hz, outputting frames for the left and right eyes alternately. Then, the user can put on the LC-shutter glasses whose shutters are closed alternately. As a result, each eye will see 60 frames per second.
Being the most notable implementation, the ELSA 3D Revelator did not really take off. This device was unhandy and had a lot of hardware and software problems. It did not support the then-popular 3D accelerators from 3dfx and were officially meant for video cards made by ELSA itself.
In the following years this technology was almost forgotten. CRT monitors died out like dinosaurs (they did have something in common in terms of size and weight) whereas new LCD monitors could not support a refresh rate higher than 60Hz. (each eye would only see a refresh rate of 30Hz in the LC-shutter glasses, which resulted in a strong flicker).
This situation has changed but recently. LCD monitors have evolved, making it possible to use a refresh rate of 120Hz. In August of 2008 at the NVISION visual computing conference in San Jose, NVIDIA publicly demonstrated some new stereoscopic 3D technology. While stereoscopic 3D in and of itself is not new, the devices on display at NVISION were, and featured new hardware, monitors, wireless glasses, and software. At the event, the technology was demoed on a Mitsubishi 73-inch 3D Ready 1080p-capable DLP television and new ViewSonic 120Hz LCD monitors using a number of popular games. Fast forward to today, and NVIDIA is ready to officially take the wraps off of their stereoscopic 3D technology, which is now known as GeForce 3D Vision. NVIDIA's GeForce 3D Vision product consists of a pair of wireless, rechargeable glasses, a base station / IR transmitter, and the necessary software and cables to connect the device to a PC. However, it needs some other specific hardware to function properly as well - namely a compatible monitor and graphics card.
It is worth bearing in mind that this is still cutting edge technology and that such stuff is always expensive. As time goes by those who are just behind the curve will start to catch up and the 3DVision will become a technology which is more viable beyond just the corporate or early-adopter market.
The main reason why there is no doubt about the future success of the GeForce 3D Vision glasses is that they are compatible with graphics cards and monitors from different manufacturers. As opposed to the competing technologies such as Zalman Trimon and iZ3D, you don’t have to compromise, choosing a monitor out of two models that only differ with screen size and have unassuming exterior design. Even today, the two major monitor makers Samsung and ViewSonic have provided GeForce 3D Vision compatible products. It means that Nvidia has found an understanding among first-tier manufacturers and we will surely see such monitors from other brands, especially as there is nothing technically complex about them.
And contrary to the products from Zalman and iZ3D, you don’t even have to buy such a monitor especially for stereo glasses. Samsung SyncMaster 2233RZ is quite an interesting monitor in itself for gamers as well as ordinary users. Besides the compatibility with stereo glasses, its 120Hz refresh rate ensures excellent smoothness of motion and considerably reduced visual artifacts together with a fast response time.
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