How do today's 3D glasses work

The 3D technology

How does 3D actually work? How do manufacturers use human perception to produce spatial image reproduction on the cinema screen, TV, Blu-ray or game console? What procedures are there with and without 3D glasses? What is the so-called "dollhouse effect"? Everything you need to know about 3D and stereoscopic vision can be found here ...



Fig. 1: Quo vadis 3D? With glasses or without glasses? - hype or not?

 

When it comes to the hype cycle model that Jackie Fenn has developed from the renowned American consulting firm Gartner, the short 3D hype of the TV industry follows, which Avatar and Co. soon causes disillusionment. Establishing 3D rendering in the living room at home would be the most natural thing in the world. Humans developed sculpture to spatially represent gods, heroes, rulers and important contemporaries. During the Renaissance, the perspective that had already been developed in the Greek Classical period was rediscovered in order to be able to give paintings space. Today's 3D playback technology certainly has its shortcomings (more on that later), but today's large-format HDTV 3D televisions come very close to people's dream of lifelike reproduction of scenes and events in their own four walls.

You can find more information about 3D technology here: The MPO image format

 

 

Before we try to estimate the further development progress of 3D, we first consider the geometric basis of spatial vision for a better understanding.

Because the two eyes are horizontally separated by the interpupillary distance, we see the same visual scene from two different starting points and thus from two different perspectives.

Fig. 2: The geometry of spatial vision. Horizontal section through the right (AR) and left eye (AL) seen from above. (Own drawing after Tyler C.W. 2004 Binocular Vision; in Ponco R. et.al. 2008 Stereopsis)

Figure 2 illustrates this with a horizontal section through the right (AR) and left (AL) eyes, which is seen from above. In order to see the arrow sharp and three-dimensional, the eye muscles swivel the eyes into the respective angle (convergence) and the muscle of the eye lens ensures a sharp image by setting the correct focal length (accommodation). As we can see, the images of the arrow on the retina of the right and left eyes are different. Every technical 3D process that wants to enable a reproduction that is true to the original must ensure that these two different perspectives are again offered to the correct eye.

 

Many technical 3D processes have been developed in the course of film and television development history. In Fig. 3 you can see a compilation of the methods that were used in television technology for 3D moving image reproduction or are used today. The processes used today are marked in red. Roughly one can make a division into procedures that require glasses for viewing and techniques that do without glasses.

Fig. 3: Technical process for 3D moving image reproduction

 

The procedures with glasses are explained in more detail below.

Anaglyph technique

The brothers Louise and Auguste Lumiére, who had already developed the first functional cinema projector, officially showed the first stereo film of a few seconds in France in 1903. It had the title "L'arrivée du train". Martin Scorsese incorporated this film document into his new 3D film "Hugo Cabret", but not in 3D. The Lumière brothers used the anaglyph technique, which had already been developed for stereo photography. Color filter glasses (red / green or red / cyan) ensure that the left eye can only see the image from the left camera and the right eye only the image from the right camera. Either two film projectors are used for the left and right pull-out with the corresponding color filters or a projector, which then projects a film strip onto which the right and left images in the corresponding colors (red / green or red / cyan) were copied. With the introduction of color television, anaglyph technology was also possible in the home. In 1982, for example, ARD showed a series of 3D picture broadcasts in its 3rd programs. Since this technology in principle is only well suited for black and white reproduction and can only provide very poor color reproduction, it no longer plays a role today. Of course, it has to be used when viewing treasures from the early days of 3D film.

Psycho-optical effects (Pulfrich effect)

The Pulfrich effect was cultivated for television because, in contrast to the anaglyph technique, it enabled the usual PAL color image quality, only required very inexpensive glasses and shows a normal picture when viewed without glasses. With regard to the movement required for the effect, it is not relevant whether the object or the recording camera is moving. In the early 1990s, for example, the private broadcaster RTL incorporated scenes in its "Tutti Frutti" series in which the female actresses acted on a revolving stage. Since the process only provides depth information when the object or camera is moving, it is a professional process for 3D TV sets not suitable.

Shutter glasses (LCD light valve)

Liquid crystal shutters have been fast enough to be used as light valves for 3D film and 3D video technology since the early 1980s. With this method, the image for the left and right eye is shown sequentially one after the other (see Fig. 4).

Fig. 4: The shutter glasses process.
The glasses only allow the corresponding camera image to pass through for the left and right eyes.

 

 

The shutter glasses are controlled with a wireless synchronous signal and the built-in control electronics ensure that the correct eye then has a clear view. In the case of use in the cinema, the expensive glasses, which also contain a battery or a rechargeable battery, are a major disadvantage. A normal projection screen can be used in the cinema because polarized light is not used. So that it can be used, for example, in small arthouse cinemas or in the semi-professional area with correspondingly small audience numbers.

In the case of 3D televisions, e.g. At the moment, a lot of manufacturers are focusing on active LCD shutter glasses. Today it is the only process with TV sets on the German market that can also reproduce the full HDTV resolution (1920x1080) in 3D mode. The higher cost of glasses is not as relevant given the small number required in the home environment. The switchover of the shutter glasses between left and right original must be done with at least 50 to 60 Hz in order to avoid flickering. This means that the display must then be controlled with at least 100 to 120 Hz. Since LC displays are already operated at 100 or 200 Hz or 120/240 Hz for reasons of optimal motion reproduction, this requirement is not a problem. In order to avoid problems with double contours due to cross-talk of the images in the darkened eye when using LCDs (Ghosting see 4.), many device manufacturers who use LC displays rely on 200 Hz technology. This gives enough time to ensure that while the shutter glasses are open, only the correct image in each case reaches the corresponding eye. Together with a 3D Blu-ray player, which is connected to the 3D TV set via an HDMI connection (version 1.4) and in the so-called "frame packing format", a left and a right image in succession transmits at full HDTV resolution (1920x1080) at 24 frames per second each, today's 3D TV sets with shutter glasses achieve the best possible 3D playback quality in the home.

 

Examples of glasses: The glasses in the middle should look familiar to you, they are Real D 3D glasses, as they are used in most cinemas that do not use shutter technology and work with polarized light that is reflected in the cinema by a silver-coated screen . The glasses on the right belong to a JVC DLA-X3 projector, the glasses on the left are a counterpart from Sony. Note: The light loss behind Real D 3D glasses is approx. 32 percent, if you simply put two of these glasses on top of each other, you can visually see roughly the light loss that shutter glasses have. In this way, you can check in advance how the loss of light is expressed in the shutter process and to what extent what is seen through the glasses then appears darker. However, this is only intended as a guide, the loss of light due to the shutter, i.e. the opening and closing of the glasses, is even somewhat greater in the shutter process.

Polarizing filter

In the history of 3D cinema films, color 3D film playback was only possible with the help of polarization filters. The image for the left and right eye is projected onto the screen by a projector each with polarization filters with different polarization planes (horizontal, vertical) in front of them. There is also a method in which only one projector is used to sequentially project the left and right images. A polarization filter is then connected upstream, which quickly switches between the two polarization planes. The viewer wears glasses with a horizontal and a vertical polarization filter so that each eye can only see one image. The screen must, however, be a "silver screen" (aluminized surface), since other screen materials do not maintain the plane of vibration when reflected with polarized light. However, perpendicular (crossed) polarization filters still have a luminance transmission of approx. 10 to 15%, so that there is little crosstalk from the original image to the right eye and vice versa. When the head is tilted, the polarization axes of the glasses filters are rotated so that crosstalk also occurs. To avoid this, circularly polarized filters are used today in 3D cinema projection described above, but now the plane of oscillation of light is circular (clockwise and counter-clockwise).
The greatest advantage of the polarization process is the inexpensive passive glasses. This is the ideal solution for screenings in large cinema halls with a large number of spectators. In the case of the 3D home television set, as in a variant of the cinema projection, one could also imagine a large switched polarization filter in front of the display (LCD or plasma). The left and right images could then be displayed sequentially one after the other and the filter switched accordingly. As in the case of the cinema, the viewer then wears simple passive polarization glasses. Unfortunately, however, large-area, quickly switchable and inexpensive polarization filters that could be attached in front of the flat screen are not available. That is why the idea of ​​a line-sequential left-right image display was taken up. A polarization filter is applied to the flat display, which changes the polarization direction from line to line. The filter does not need to be switchable. The video signal processing (scaler) in the 3D TV set must then ensure that one line of the left and then the right image is displayed alternately. As in the cinema, the viewer then wears passive polarization glasses. The principle is shown in simplified form in Fig. 5 using only eleven lines. The big disadvantage, however, is that the resolution is halved in the vertical direction. In the case of high-definition television (HDTV), this results in 1080 lines / 2 = 540 lines. This is the vertical resolution of the previously common Pal television.

Despite this disadvantage, there are manufacturers who use this principle in their 3D TV sets in order to be able to offer inexpensive and easy-to-wear glasses. In order to circumvent this disadvantage of the reduced vertical resolution, LG has now presented devices with a 4k display at the Consumer Electronic Show in Las Vegas. This means that instead of the usual HDTV resolution of 1920 x 1080 pixels (approx. 2 megapixels), this display has four times the number of pixels of 3840 x 2160 pixels (approx. 8 megapixels). In 3D operation with the polarization changing line by line, the vertical resolution is halved. However, 2160/2, i.e. 1080 lines, remain, i.e. the full HDTV resolution is retained.

Fig. 5: The principle of the polarization filter process is greatly simplified using only 11 television lines.

 

More detailed descriptions of the procedures without glasses follow.

Autostereoscopic procedure

Fig. 6: Principle representation of the glasses-free procedure for 2 views (left and right). (Own drawing after Holliman N. (2005) 3D Display Systems; University of Durham)

 

A basic principle for this was patented as early as 1912 by the Swiss ophthalmologist Walter R. Hess as the "Lenticular Foil Stereogram".

When this technology is applied to 3D TV sets, a lenticular lens film (Fresnel lens filter film) is applied directly to the flat display (LCD or plasma). The display is then controlled in such a way that vertical stripes of the left and right image follow one another (which, however, halves the local resolution in the horizontal direction). The distance between the eyes ensures that each eye gets the right picture. In practice, however, there is a very small area (small sweet spot) in which the image can be correctly viewed stereoscopically. For this reason, systems were developed that capture the viewer's eyes with a camera and determine the distance and interpupillary distance and then move the lenticular lens plate mechanically. Or as in the case of a notebook that Sony showed at the 2011 radio exhibition, in which the left-right pixel pattern on the notebook display can be readjusted with the camera information in order to be able to maintain the 3D impression when the head is moved. These systems cannot be used for a 3D TV set that can be used in the home. For this reason, a method was developed that uses several views and thus enlarges the angular range from the 3D accordingly (large sweet spot).

Fig. 7: Principle representation of the glasses-free procedure for 5 views (left and right). (Own drawing after Holliman N. (2005) 3D Display Systems; University of Durham)

 

In today's realizations eight, nine or even 15 views are used. If one were to do this according to the principle of the exclusively vertically oriented lenticular lens film, the horizontal resolution (number of pixels) would be reduced by a factor of nine for nine views, which would lead to a very modest image quality. This is why, for example, when there are nine views, they are distributed horizontally and vertically in a pattern. The lenticular sheet must of course be adjusted accordingly. With this arrangement one can then achieve a loss of resolution balanced in the horizontal and vertical directions by a factor of three. In the case of an HDTV picture with 1920 x 1080 pixels, this still means a reduction to 640 x 360 pixels and is therefore even somewhat worse than standard PAL quality. In order to be able to realize high-resolution television (HDTV) in 3D, flat displays with multiple HDTV resolutions must be used. There are already LC displays with multiple HDTV resolutions, but due to the high costs they could only be used for very special applications (e.g. medical technology).

Toshiba presented its first glasses-free 3D TV set at the 2011 radio exhibition. These devices use a display with four times the number of HDTV pixels (3840 x 2160 pixels or approx. 8 megapixels) and are based on 9 views. Despite the panel with four times the HDTV resolution, 9 views only result in a resolution of approx. 0.9 megapixels, i.e. less than half the number of HDTV pixels. In other words, in order not to drop in image sharpness (resolution) in 3D operation, the display used would have to have at least 9 times the HDTV resolution. The fact that flat display manufacturers are working on such panels could also be seen at the 2011 radio exhibition. Sharp showed a foretaste of a future Super Hi-Vision system with 16x HDTV resolution. In conclusion, however, it can be stated that this autostereoscopic method (based on n-views) is the only glasses-free 3D technology for the home that has the potential for broader implementation in the near future. For the sake of completeness, it should be pointed out that there is a second autostereoscopic method based on the parallax stereogram. However, the application of this technology to flat displays (LCD, plasma) leads to a strong reduction in image brightness, which is caused by the shadowing of the barrier required for this principle (e.g. slit diaphragm). This is why this principle is not used in 3D TV sets. However, it is used for small displays for small "handheld" devices in the gaming and mobile phone sector.

Finally, the advantages and disadvantages of the methods used in 3D television technology are summarized in Fig. 8.

Fig. 8: Advantages and disadvantages of the methods used in 3D television technology.

 

3D cinema and 3D television

The main problem is that when viewing natural originals, a change in accommodation (focusing of the eyes by changing the lens focal length) is accompanied by a change in convergence (changing the angle of convergence of the two eyes by the eye muscles). If we look at a virtual 3D scene on a cinema screen or on a television screen, the focus point is fixed on the projection plane. The setting of the convergence angle is determined by the recording and projection (see Fig. 9).

Fig. 9: 3D projection onto a flat surface. (Own drawing after Hodges 1992; in Howard I.P. 2002 Seeing in Depth)

This conflict between convergence and accommodation puts a strain on the convergence system, which in rare cases can lead to eye strain and nausea. This has at least been reported by users of 3D virtual reality systems (Howard 2002). In order to safely rule out risks and concerns, further scientific research must certainly be carried out here. In order to avoid overexertion of the convergence system of the viewer by over-cultivating the depth effect, it is essential not to enlarge the left-right camera distance beyond the eye relief when recording. A change in the angle of convergence during recording should also be handled extremely moderately.

Since today almost exclusively processes involving glasses are in commercial use, when designing the glasses, attention should be paid to ensuring that glasses wearers who then have to wear two glasses on top of each other do not experience any reflections or optical errors when stacking them. In general, the use of polarization or shutter glasses means a reduction in brightness. This is not so important in the cinema because the cinema is darkened. In the case of 3D televisions, you should make sure that the device has a sufficiently large reserve of brightness so that 3D television is possible in full daylight.

3D television and the dollhouse effect

The local limit resolution of the human eye, which results from the density of the cones in the fovea, certainly varies somewhat individually and is approx. 1 to 2 minutes of arc. If we assume an average resolution of 1.5 arc minutes, this corresponds to 0.025 °. With this value, the number of lines in the television system and the screen diagonal of the television set used, the optimal viewing distance can be determined using elementary angle functions. The line structure or pixel structure in flat panels is practically on the threshold of visibility and therefore does not interfere. This gives you the best possible telepresence, i.e. the image size fills the viewer's field of vision as far as possible. If we assume a TV set with a screen diagonal of 1.07 m (42 inches), the result for standard television (SDTV) is a viewing distance of about 2.60 m (approximate value about 5 times the picture height). With high-resolution television, this is the only consideration for 3D TV, there is an optimal viewing distance of approx. 1.30 m (approximate value 2.5 times the image height).

For rough calculations, the picture height of televisions in 16: 9 format (standard for HDTV-compatible devices) can be assumed to be half the diagonal. As can be seen easily, a viewing distance of 2.5 times the picture height (or 1.25 times the screen diagonal) is not maintained in the domestic landscape when viewing high-resolution television. When viewing 3D films, this leads to the so-called "dollhouse effect". This means that when taking wide-angle shots, the objects viewed are so small that they are not believed to be real With its huge screens, it is of course superior. In the home, you should therefore choose a device with a diagonal that matches the viewing distance, or even a 3D HDTV projector with a correspondingly large projection screen.

3D televisions and left and right channel crosstalk (ghosting)

As already mentioned, active LCD shutter glasses are used for the most part in 3D televisions that are in series production today. The opening time of the glasses must be precisely adapted to the display time of the respective left or right image template on the television screen. If this is not optimally adjusted, the left and right eyes receive a weakened image of the image intended for the other eye. This then makes the disparity of the two images visible, i.e. one sees double contours.


BUROSCH Crosstalk test images in laboratory use are used to analyze crosstalk

 Example of a real image with largely perfect 3D image reproduction. The vertical, high-contrast lines do not show any double contours = optimal crosstalk value.

 The same real image with poor 3D image reproduction approx. 18% crosstalk. Note the clear double contours particularly visible on the lantern and on the rain drainage pipe running vertically downwards = poor Corsstalk value.

 

3D televisions that calculate 3D from normal 2D templates

It is basically an approach that has been tried again and again when introducing new standards. When audio stereophony was introduced, attempts were made to convert mono signals into (pseudo) stereo signals. When high-definition television was introduced, it was claimed that higher-definition components could be calculated from a standard TV signal. And now, with the introduction of 3D TV, attempts are being made again to calculate depth information for flat 2D recordings. What all these attempts have in common is that, in principle, they cannot work. There is no technology in the world that can add information that was not captured when it was recorded. In the case of 3D TV, an attempt is made to use object recognition algorithms to capture individual objects and people from the flat image and then assign them an artificial depth. When implemented in consumer 3D TV sets, due to the "real-time conditions" and the very limited computing power, this leads to a so-called cardboard cut-out phenomenon. In other words, objects appear to have been cut out and placed in front of the background this has nothing to do with natural depth reproduction.

The procedure described above should not be confused with the procedure for computer graphics. In the studios, cartoons and animated films are produced purely synthetically or through acceptance from models on a mathematical basis. Depth information is also built into these mathematical maps. However, these cartoons and animated films cannot claim that they reproduce the real world that surrounds us as naturally as possible and without falsification.

"Beauty lies in the eye of the beholder" is what Shakespeare says. When considering buying a 3D TV, the only thing to do is trust your own eyes. This means that you should make a picture comparison between the devices offered at your dealer with a corresponding picture template that you know and that you can use again at any time. There are also experts who offer 3D test Blu-rays or test images for downloading for this purpose (e.g. at http://www.burosch.de).

If one looks at the attempts to establish 3D films in the film industry, peaks in the 50s, in the 80s of the last century and now from 2009 to today are noticeable. Two facts can easily be deduced from this. The peaks can be observed every generation, i.e. each new generation gets to know this technology for the first time in the cinema. And secondly, these attempts followed a decline in cinema attendance due to new media in the home area. In the 50s through the triumph of television in the USA. In the 80s the widespread spread of color TV sets with large CRT screens and a large number of receivable programs (private TV providers) and at the end of the first decade in the new millennium the establishment of large flat screens and high definition television (HDTV) in living rooms.

In my opinion, the content of the respective 3D film offer should not be ignored. In the 1950s, the range of 3D films with horror and science fiction films such as Jack Arnold's "It came from Outer Space" was mainly aimed at adults. In the 1980s, exploitation films and a lot of eroticism were tried out (eg Emmanuelle 4 in 1984). And the latest attempt (2012) are mostly computer-generated animation and action films for today's mostly young cinema audience. What has changed, however, is that well-known directors are now also using 3D film technology as a means of artistic expression I would like to show mine with three examples. First there is the wonderful homage of the director Wim Wenders to Pina Bausch. Anyone who sees the portraits of the company members while they are telling their memories of Pina must admit that 3D is a necessary artistic means of expression. Second, Werner Herzogs "The Cave of Forgotten Dreams". Only 3D technology can reproduce the up to 35,000 year old rock carvings in the Chauvet Cave as the Stone Age artists thought them to be. They used elevations and depressions in the rock walls to give their animal drawings a three-dimensional effect. And third, Martin Scorsese's latest masterpiece "Hugo Cabret". Without 3D technology, all the mechanical clocks and automatons would appear flat in the truest sense of the word.

This means that the chance is huge that 3D technology will become firmly established this time and, in addition to the event character of blockbuster 3D films, a broader audience with more demanding subjects will be able to open up. In the German home sector, the 3D Blu-ray will initially remain the most important program source for the 3D-capable flat-screen TV, apart from the niche market of self-recordings with consumer 3D cameras and 3D camcorders, because the public and private broadcasters have with the introduction from HDTV to carry huge investments. That is why it will probably not be possible to invest in large amounts in the acquisition of 3D cameras and 3D studio infrastructure in the medium term. Especially since the currently The methods used for television transmission for reasons of bandwidth economy and backwards compatibility with SAT receivers on the market, e.g. work in side-by-side mode, which results in the reduction of the horizontal resolution by half (instead of 1920 pixels, only 960 pixels per TV line). This is then only slightly more than the standard TV resolution (DVD 720 pixels) and thus counterproductive to the introduction of HDTV. Furthermore, channels in which 3D is transmitted in side-by-side mode are not backwards compatible, i.e. TV sets that do not have a 3D function would show the compressed left and right image side by side.

For this reason, the MPEG-4 MVC standard introduced for Blu-ray will also prevail in the long term for 3D television broadcasting and will be installed in SAT receivers and cable TV receivers. Furthermore, the question remains whether larger parts of the consumers are willing to wear glasses when watching TV. Because only the use of shutter glasses or polarizing filter glasses in conjunction with a 4k panel guarantees 3D playback with full HDTV resolution. The devices available today with glasses-free processes (autostereoscopic) do not achieve HDTV resolution and also leave a lot to be desired in terms of depth effect. On the other hand, the use of glasses does not mean that the introduction of future high-quality glasses-free 3D TV sets will call into question the entire current system. The current standard MPEG-4 MVC (Multiview-Video-Coding-Format), in which different images are recorded for the left and right eye, saved on the Blu-ray and output via the player via HDMI, will continue to exist in the future - Only the representation of the image on the display will change and the glasses could gradually disappear. The prerequisite, however, is that the costs for super-high-resolution displays can be reduced accordingly, thus enabling the construction of affordable 3D TV sets without glasses. Today's innovative buyer of 3D Blu-ray films need not fear that they will no longer be able to use their discs with new 3D display processes.

Further information: http://burosch.de/technik/403-das-raeumliche-sehen.html

Holliman, N. 3D Display Systems, Department of Computer Science, University of Durham, Durham 2005

Howard, I.P. Seeing in Depth, Volume I Basic Mechanisms, University of Toronto Press, Toronto, 2002

Howard, I.P. Seeing in Depth, Volume II Depth Perception, University of Toronto Press, Toronto, 2002

Ponce, R. (et al.) Stereopsis, Current Biology, Volume 18 No 18, 2008

 

Konrad L. Maul - author of this report

Konrad L. Maul worked in television development for 37 years, including 30 years in a managerial position at Grundig. As division manager, he was responsible for the first 100 Hertz TV set. From 2001 to 2008 he was in charge of television development for a large German TV manufacturer. This makes him one of the most experienced and high-profile TV developers in Germany.

http://www.m2counselling.de

COPYRIGHT, All rights reserved, Konrad L. Maul, Dipl.-Ing. (FH), 90473 Nuremberg

 


 

In addition to the conventional anaglyph technology with the red-green glasses or the polarizing filter technology in the world of projectors, the shutter glasses technology is the best known and best solution for the discerning 3D home cinema user. Unfortunately, this shutter glasses technology also has a few technical problems: The so-called cross-talk disturbs the image quality. And to control this negative influence and, if necessary, to optimize it, there are the 3D crosstalk test images.



Vertical, high-contrast lines do not show any double contours.
Fig. 1: Optimal crosstalk value
Please note the clear double contours particularly visible on the lantern.
Image 2: Bad crosstalk value

When it comes to 3D technology, shutter glasses are state of the art in 2012. Unfortunately, crosstalk interferes with what are known as ghost images in the other eye. Image information in the left eye shows up in the right eye and thus reduces the image quality. Please note the annoying double contours of the lantern in Figure 2. With high contrast values, i.e. black vertical lines in front of a light background, high crosstalk values ​​are very noticeable. Measuring this poor image quality is very easy with the crosstalk test images developed by us. Corresponding to the segment sections of a clock, the percentage value can be defined on our crosstalk test images, the percentage by which the image information from the left eye has an influence on the other eye. This value depends on the luminance contrast ratio and also on the chrominance influence.
Laboratories and industrial companies are happy to receive individual information from us about measurement technology
Please also note our corresponding technical documentation for download. Of course, our 3D crosstalk test images can also be downloaded from www.burosch.de

Reference test image for measuring the 3D crosstalk value at 100% luminance contrast ratio

50% contrastR 100% chromaG 100% chroma
Reference test images for measuring the 3D crosstalk value at 50% luminance contrast ratio
Reference test images for measuring the 3D crosstalk value at 100% chrominance RGB contrast ratio.


Of course, we offer the 3D crosstalk test images developed by us in all processes such as side-by-side, top button, as JPG files, as MPO files and also Blu-ray Disc.
Please just get in touch with us. We would be happy to advise commercial users.

 


 

The suppliers of televisions and Blu-ray players are rolling over product announcements. The answer is simple: Because you can. The Blu-ray disc with its enormous storage capacity offers space for the additional data that the ever faster switching flat screen displays allow, like in the cinema, the alternating representation of the perspectives for the left and right eye.

It is not decisive whether the consumer demands it at all. But it is assumed, and rightly so. 3D images and especially moving 3D images have always been a special attraction. In the past, children were given the Viewmaster peep box, in which 3D slides rotated on a disk, while adults enjoyed spatial images from space in Imax cinemas. And the record records for "Avatar" and "Alice in Wonderland" speak for themselves.

The basic principle of spatial vision

Just as humans have two ears for spatial listening, they use their two eyes to grasp the arrangement of their surroundings. The eyes are about 6.5 centimeters apart, and this is exactly how you should position two cameras for 3D recordings. The difficulty lies in getting these two perspectives to the two eyes. Because only then does the viewer get the incomparable feeling of depth that is rarely found in normal pictures.


A 3D misunderstanding affects the systems. The chain of three-dimensional moving image processing consists of different technologies that have only one thing in common: the two perspectives are recorded, transported and displayed. The type of storage on a Blu-ray has nothing to do with how the screen displays the two perspectives. For over 20 years there have been processors and image memories that allow any conversion from one format to another.For 3D with full HD resolution, the effort is twice as high as for normal HDTV, but chips for 200 Hertz already master the necessary work speed. The 3D glasses have nothing to do with the 3D Blu-ray - unless the film is saved using the outdated red-green process. The player and screen also work together without any problems if they have a common transmission format. The electronics do the rest.
 

10 facts about 3D

  • Films like "Monster House" or "Chicken Little" have achieved three to four times their normal sales in 3D cinemas.
  • This year around 30 feature films in 3D will hit the big screens, next year around 50 films.
  • 3D processes with colored glasses are out of date, they strongly distort the colors.
  • The 3D standard for Blu-ray is suitable for any type of screen that can display 3D and accept the appropriate signals - regardless of the technology used.
  • All current 3D processes work with glasses that are adapted to the respective screen.
  • Displays for 3D without glasses are possible, but either blurry or only suitable for a viewer.
  • The majority of TV sets with 200 Hz LCDs and plasma technology will soon be 3D capable.
  • 3D display is associated with a high loss of light, which means that it degrades the energy efficiency of the screens.
  • It is possible to convert normal TV pictures or films into 3D, but the results are worse than real 3D.
  • 3D does not completely correspond to natural vision, as the eyes do not have to be adapted to near or far and the images do not change when the head is moved.

This is how 3D is produced

Three-dimensional films can be produced in different ways. The result must always consist of two perspectives, which look like the viewing angles for the right and left eye. The three current options are:

Calculation in the computer; Most of the 3D strips in the cinema come directly from the computer, where all the data is already available in three dimensions. Then you only have to calculate twice, which means a lot of effort, since even high-performance computers have been working on one version for several weeks.

Recording with two cameras side by side; Real scenes are filmed in such a way that the two cameras are placed at eye distance from one another. But depending on the optics used, such as telephoto or wide-angle, you have to vary it so that it looks natural. Visual effects are particularly problematic: if, for example, the sinking Titanic is only a tenth of its real size, the camera distance must also shrink to a tenth, otherwise the steamer looks like a toy. At the moment there are no cameras available that are ready for 3D by default. But they should come onto the market in the course of the year.


This is what 3D looks like in the cinema

The endeavor of the Hollywood studios was to realize the 3D experience at home as equivalent to the cinema as possible. The number of pixels is almost exactly the same, the cinema files have either 2,048 x 858 pixels (for films in 2.39: 1 format) or 1,998 x 1,080 (for films in 1.85: 1 format). The same applies to the frame rate, since 48 Hertz is used for 24 frames per second twice. Just like in the living room or home cinema, there is a uniform format for storing 3D images in large cinemas, but many different technologies for presentation.
In principle, every projection method that is used in the cinema can also be used at home. The company Xpand uses shutter glasses in the cinema similar to those required for modern LCD or plasma screens. RealD in the cinema, on the other hand, uses polarized filter glasses that do not work with the new televisions, only with older LCD screens. The Dolby process with different color spectra can be used at home with additional filters with two projectors. In contrast to Blu-ray, digital cinema has a larger color space and higher color resolution. The compression is less, both perspectives are independent of each other.


This is how 3D works on Blu-ray

New Blu-ray players are required for true 3D in the cinema at home. Older devices play the new 3D films, but only in two dimensions. The new 3D profile of the Blu-ray Disc Association (BDA) makes coding in Multiview Video Coding (MVC) mandatory. This means that in addition to the normal 2D data stream that contains the signal for the left eye, another stream for the second perspective is stored. It contains the differences for the right eye, so no further full picture. But from this two full HD signals with 1,920 x 1,080 pixels and 24 frames per second (exactly: 23.976) can be calculated. Storage at 1,280 x 720 at 60 Hertz (59.94) is also possible, which is suitable for sports recordings.
Other formats are not permitted, i.e. neither standard resolution nor 50 Hertz or interlaced (fields, 50i or 60i). You have to forego picture-in-picture bonuses in 3D operation, but otherwise the discs cannot be distinguished from normal Blu-ray editions.
Connections are critical. Nothing is stipulated here in the 3D standard, so the strict provisions of the AACS copy protection apply. And that means that the only possible interface is HDMI. The protection of analog signals is too holey for Hollywood studios, apart from that, 3D is not standardized via such interfaces. All screens that require direct control, for example at 120 Hertz, are therefore unsuitable for 3D from Blu-ray.


3D on the Sony PS3

It's no secret: both the 3D standard for Blu-ray and HDMI 1.4 have been tailored to what the Playstation 3 from Sony can already do. Even the Sony competition had no objections, since with the PS3 as the player, a large 3D market immediately exists. Details are still unclear, but as things stand at the moment, every owner of a PS3 can assume that they will have a full-fledged 3D player for Blu-ray discs from July. Then namely, the upgrade should be played via software. Some games can already be enjoyed in 3D today (you can read about how well on page 26).

Concerns that the 3D quality might not match that of other players seem unfounded. Because the cell processor can decode two video streams in full HD resolution. The output takes place at
Blu-ray with 24p, where both images are packed into one frame; this is already provided for in the HDMI chip that is in the PS3. It remains to be seen whether the Playstation can automatically communicate the 3D format to the television.


This is how 3D comes to television

While there is a worldwide standard on Blu-ray, there is no such thing for three-dimensional television. Nevertheless, numerous broadcasters (including Sky in England) have already announced that they will be launching special 3D channels in the course of the year. What they have in common, however, is that 3D processes are used here, which rule out that the program can also be viewed with normal televisions - so they are not backwards compatible. The perspectives are packed into a single image, which has the advantage that it can be transmitted using existing TV technology, from satellite transponders to home set-top boxes.

The preferred 3D variant is likely to be the so-called side-by-side method, at least for the beginning. If you look at the picture on a normal screen, you see the two perspectives side by side, both squeezed sideways. The 3D electronics on the screen must therefore recalculate them and assign them to the two eyes. At full HD resolution, each image then only has 960 x 1,080 pixels. The result can be improved if the checkerboard scanning developed by Sensio is used; At first glance, this procedure cannot be distinguished from side-by-side, since otherwise it could not be transmitted in MPEG.
In the medium term, one can also expect set-top boxes that understand the MVC codec as used on Blu-ray. Then, in the case of 3D broadcasts, the message is simply displayed that glasses can now be put on. An extra channel for 3D is then no longer necessary, and the resolution is no longer limited.


This is how 3D televisions work

What all new 3D televisions have in common is that they work with fast image changes and shutter glasses that sometimes activate the left and sometimes the right eye. But that's where the similarities stop.

The 3D implementation with plasma screens is relatively easy. Firstly, the light cells react extremely quickly and, secondly, the electronics always switch all pixels to the next image at the same time. This makes it possible to split a 120 Hz rhythm into two 60 images per eye. However, you are again dealing with the 3: 2 pulldown, that is, the stuttering typical of a cinema when playing a film. And with TV signals, such as from Sky, you fall back on a slightly flickering 50 Hertz. Panasonic allows at least 96 Hertz for Blu-ray playback, i.e. 48 images per eye. Time will tell whether jerking or flickering is the lesser evil for the audience; On the other hand, 144 Hertz, i.e. 72 images per second per eye, are not possible.

It becomes more difficult with LCD, where panels with 100 or 120 Hertz are not sufficient. Because the pixels are switched one after the other from top to bottom, plus the still relatively slow reaction of the liquid crystals, so that there is not a long enough period of time in which the glasses can open. That is why the first manufacturers are using panels with 200/240 Hertz, which, however, fall back to 120 Hertz in 3D mode, i.e. 60 per eye. Real 240 Hertz, i.e. 120 images per eye, can only be achieved with significantly faster panels and pulsating LED backlighting. These devices are then usually specified with 400 or 480 Hertz.

Another technology uses polarized filter glasses, which, however, require a filter film on the screen. That makes the TVs expensive while the glasses are cheap - good for pubs or other public screenings. Polarizing filter glasses cost around one euro, prices above 100 euros have been announced for shutter models.


This is how 3D glasses work

A common misunderstanding is to blame the glasses for the 3D effect. That may have been true with the outdated red-green process, with modern systems an exact adaptation of the glasses to the representation of the display is necessary. Otherwise there will be interference such as crosstalk, in which the other perspective can still be seen as a ghost image, or flickering. Since there are only a few manufacturers of shutter glasses, glasses not supplied by the TV manufacturer should also work in most cases; but optimal results are not guaranteed.


Those are the disadvantages of 3D

The topic of 3D is in stark contrast to the trend of energy saving. Because the efficiency drops enormously, i.e. the ratio of light output to amount of electricity. As a matter of principle, 3D technology halves the brightness per eye, in addition to which there are further losses through filters and glasses, so that the actual value is somewhere between 25 and ten percent. The 3D image is therefore considerably darker.
But real 3D enjoyment should take place in the dark, as all lights in the room significantly disrupt the effect, for example through reflections in the glasses and on the front glass. Even if the light output of the umbrella has to be turned up a bit in 3D operation, this can largely be compensated for by saving on room lighting. In addition, you need less brightness on the screen in the dark anyway.
In addition: two-eyed vision is not perfect either, the influences of head movement and focusing of the eyes are missing. So not everyone enjoys 3D right away.

Record 3D

In Japan, Panasonic has already presented the first Blu-ray recorders that are 3D-capable, namely the DMR-BWT1000, 2000 and 3000 models. These are devices that can record normal television or play 3D Blu-rays . The ability of the recorder has nothing to do with 3D television.

The 3D channel announced by the British BSkyB can be recorded with any hard disc satellite receiver for the Sky service, as it uses the side-by-side in-picture method, in which the two perspectives are squeezed together and broadcast together. Any HD recorder can record this - with Sky, however, restricted by the encryption system used. Neither a special box nor a special recorder is required for side-by-side or similar techniques. Only the screen needs to be able to display the image correctly. The BD recorders from Panasonic offered in Europe could also record 3D if, for example, the German Sky branch or the ZDF would start a channel of this type.

The situation is different if 3D is sent with additional data in the future, similar to storage on Blu-ray Disc (H.264 MVC). If the data stream is recorded directly, the second perspective is retained. However, it cannot be decoded and played back by normal recorders. Playing a Blu-ray disc with such a recording could theoretically work via a 3D player - but only if the broadcast format is one of the standards approved for Blu-ray, e.g. 720p with 60 Hertz.


3D inventor Lenny Lipton

Many of the technologies that make 3D in the living room or in the cinema possible today come from a man: Lenny Lipton, who will be 70 years old in May. He holds 31 patents in this area, and a further 40 have been applied for. He perfected the shutter glasses with the development of the so-called Crystal Eyes, but also the Z-Screen for the polarizing filter process, which is used with many DLP projectors in the cinema - the two systems that dominate in the cinema today. As a filmmaker, Lipton founded Stereo-graphics in 1980, which RealD took over in 2005. The fact that RealD is now the most important partner for 3D technology for the major device manufacturers is thanks to Lipton's developments. Since leaving RealD, Lipton has been working on a new format for 35mm film for Oculus3D. He wrote the book "Foundations of the Stereoscopic Cinema", which can be downloaded free of charge from the website www.stereoscopic.org/library.


HDMI & Co: The right connections

The connection between the source and the 3D screen is not without problems. Because if it doesn't fit, the pleasure is over before it begins; or the image appears distorted, blurred, or otherwise distorted in 2D. The main options are:

HDMI 1.4 - If the source, e.g. a Blu-ray player, and the display are connected via HDMI according to standard 1.4, there should be no problems, as both components then communicate and choose the optimal transmission format. HDMI cables with version number 1.4 are not required, a normal high-speed cable (Cat 2) is sufficient.

HDMI in older versions - Some older chipsets, such as those used in the PS3, already support the 3D formats required for Blu-ray. It is currently unclear whether the automatic identification is also possible or whether the appropriate mode has to be selected manually. Theoretically, it would be conceivable to loop through the 3D signals through AV receivers (HDMI passthrough); A scaling in the AV receiver or the display of menus is certainly not possible. If the loop through doesn't work, you have to make a direct HDMI connection from the player to the screen; then the HD audio tracks (DTS-HD and Dolby TrueHD) cannot be used, except for the Panasonic DMP-BDT300, which has two HDMI outputs for this reason.

VGA - Especially newer Nvidia cards for PCs are capable of 3D operating modes, namely in the form of 120 Hertz. Most of the time, however, 120 Hz is limited to XGA or 720p resolution, as Full HD requires too much bandwidth. Whether these three-dimensional signals can be reproduced by a television depends on the respective design and must be tried out on a case-by-case basis; The mere fact that a screen can reproduce 120 or more Hertz is not enough.

Video, S-Video - Normal video signals via Cinch or Hosiden can also transport 3D, but only as an in-picture format, such as side-by-side or top-bottom. Here, too, it depends on the screen whether it has built in a corresponding circuit. Blu-ray players do not output their 3D images via video, as there is no copy protection provided here.