Stereodisplay

Stereo display ( also: 3D display, obsolete: image projection space ) refers to the display of stereoscopic or three-dimensional images of a sense of depth through stereoscopic vision by means of a screen or a projection. A common use is the representation of 3D movies. Moreover, there are many applications for example in research, development, medicine and the military.

Types of stereo displays - distinction between stereoscopy and 3D

The technique of stereoscopic displays is to present two slightly different for the left and right eye images. The two images are then combined in the brain for the perception of depth. Although common for the term " 3D" is used, the correct term " stereoscopic ". Because there is a difference in whether two 2D images are displayed or whether an image is actually rendered in three dimensions. The biggest difference is that the head and eye movements of a viewer not result in a stereoscopic image for more information about a displayed object, one that is not, for example, view the object from the side or out of focus captured objects can not focus sharp. Holography and volume displays are examples of methods that do not have such restrictions. One can compare the whole thing with the reproduction of tones. Similarly, it is not possible to reproduce the full sound with only two speakers, it is also to talk over the top of two 2D images of 3D. Thus, although most stereoscopic displays no real 3D displays, so are all true 3D displays and stereoscopic displays, as they also meet the lower criteria.

The stereoscopic display

General

The channel separation referred to in stereoscopic viewing methods that are necessary for the separation of the left and right eye image. Each eye can only see the image associated with it. The ideal case is a wholly owned channel separation in which the right image for the left eye is completely invisible and vice versa. In case of insufficient channel separation caused ghosting, which can cloud the 3D perception, and at worst lead to headaches in the viewer. Ghost images are thus an erroneous representation where the image for the right and the left eye is temporarily visible to the wrong eye, especially in high contrast areas of the image.

Polarization filter technology

In this projection technique, the channel separation is achieved with linear ( obsolete) or circularly polarized light. There are opposite each offset Polfilterfolien before the projection lenses and the polarized glasses, the viewer. This, two projectors are used in cinemas.

To maintain the polarization state of light a metal-coated screen is required. A normal white canvas would diffuse the light again, and the channel separation would be repealed. The advantage of this projection technique is the high color fidelity of the images shown. A disadvantage of light loss by the filter used and the metallic screen.

For linearly polarized light the head while viewing the picture must be kept straight. If you hold the head to one side, the necessary for channel separation angle of 90 ° between the films changes from the projection lenses and filters in the glasses. This channel separation is no longer possible, it appear " ghosting ". This applies to both modern and Real -D method can no longer be, as they use circularly polarized light - you can move the head freely without disadvantages.

Another problem is the non-uniform use of the filters with different manufacturers of glasses, and projectors. The filters in the glasses must be suitable to the filters in the projector, otherwise there is a permutation of the channels. Applications of this technique except in the private sector in many IMAX 3D screenings and since 2009 also in many 3D theaters.

Anaglyph projection

Under " Anaglyphenprojektion " (from Greek ἀνά Ana "on ", " sequential " and γλύφω glypho " carve ", " engraving ", or " pose " ) in the original sense is understood in principle any stereo projection, in which the two sub-images at the same time on the same screen be sent ( and the polarization projection is therefore, strictly speaking, a " Anaglyphenprojektion " ), but usually is with " anaglyphisch " meant a farbanaglyphische representation: in order to separate the two frames different color filters in the 3D glasses are used, originally red in front of the right eye and green before the left. While watching the film, the red filter extinguishes the red film image and the green image is black - the green filter removes the green color image, and the red is black. Since both eyes now see different images, originates in the brain again a spatial image.

In the late 1970s Stephen Gibson improved the Farbanaglyphentechnik with its patented "Deep Vision " system, the other filter colors used: red in front of the right eye and cyan before the left. Meanwhile also the Danish company "Color Code" to its own color anaglyphs system. The Filter of the "Color Code" glasses are blue in front of the right eye and yellow in front of the left. For the feature film "Journey to the Center of the Earth " ( "Trio Scopics " ) in 2008 in England another Farbanaglyphenverfahren introduced, with green in front of the left eye and magenta in front of right.

Interference filter technology

The interference filter technology has been developed by DaimlerChrysler system for stereoscopic playback., The system sold by the INFITEC GmbH. The company DOLBY Inc. shall follow the procedures under the name Dolby 3D. It works on a light wavelength filter system. For each eye, a part of the perceived as red-green- blue of the eye wavelengths of the other eye is respectively transmitted and very effectively blocked. Here, the primary colors of the images are thus reduced for the left and right eye each have different non-overlapping wavelength ranges. In this case, the procedure for the viewer seems to be working color-neutral, ie there is no visible color change.

In this analysis technique, the head is arbitrarily tiltable, and it is needed no silver screen. Therefore, the method is also used in planetariums used. Lenses and filters are made of coated fused silica and are comparatively expensive. This method also requires a video processor that changes the color components of the left and right view in order to compensate for the color distortion that flow basically limited by this method again. This video processor is already installed in most projectors. Initially, existing differences in color by using different spectral regions for the primary colors red, green and blue in the left and right eye INFITEC systems are fully compensated by image processing, in the newer. This is based on metamerism, which makes it possible to produce the same color impression in the eye from different spectra. This method is suitable only for projections, but not for the printing of 3D images.

Shutter technology

With this method, both images are sequentially projected onto the white canvas. So 48 images need to be brought to the big screen for a movie at 24 frames per second at the same time, which is no problem for modern projectors. To avoid flicker, higher frequencies are usually selected, each individual image is displayed several times. The projector is during the presentation via infrared signal transmitter, which are located above the screen, control pulses to the costs borne by the viewers shutter glasses. These glasses darken each reciprocally the built-in LCD glass and thus ensure that each eye only sees the image intended for itself. Advantages are the high color fidelity and usability of a normal screen and the independence of the head tilt of the beholder. In addition, such a system despite the higher cost of shutter glasses to a certain audience size more cost-effective because, unlike the polarization method is omitted neither a projector nor a second polarizing filter for the projectors a metallized screen are still required and the synchronization overhead.

The " 3D -ready" home theater projector (mostly DLP projector) is the HDMI 1.3 connection is generally supplied with a 120 Hz 3D video signal from a 3D -compatible PC graphics card and projected as 2x60 Hz 3D video sequentially in time. In addition to matching 3D shutter (eg NVIDIA 3D Vision with its own USB infrared transmitter ) you can possibly use inexpensive so-called "DLP -Link" shutter glasses that are synchronized by a projector - white pulse between the video images and therefore no infrared require transmitter. Only 3D projectors with HDMI 1.4a connector can be fed directly with 3D HD signals from a 3D Blu -ray players, HD broadcasts.

Autostereoscopy

When autostereoscopy no glasses for viewing spatial needed. An early application was the projection to " wire mesh screens ," which was first held in Moscow in 1930. Such a mechanical image separation system was postulated in 1906 by Estanawe who suggested a fine grid of metal slats as a canvas. In the projection, the viewer must be placed very precisely in front of the screen, otherwise can not see the specific image for each of them the eyes. The system was improved by Noaillon who ordered the grid to the viewer inclined and who are now radial grid strips easily reciprocated. Further developed the system of Ivanov, who used instead of a mechanical parallel grid 30,000 very fine copper wires as canvas was. The elaborate process did not achieve mass production. Only one cinema was rebuilt for the system, the Moskva in Moscow, and even there only a few films have been shown in this procedure, such as 1940 Zemlja Molodosti, Koncert ( The Land of Youth / concert ) and 1947 the Russian movie Robinzon Kruzo did better after all, more than 100,000 spectators.

Meanwhile autostereoscopy find again new applications, such as the Nintendo 3DS, mobile phones, computer screens and televisions.

Head - Mounted Display

Head - mounted displays or video eyeglasses are worn before the eyes visual output devices, which are usually separate displays for the left and right eye in place and the two stereo images can be viewed as direct of each eye. See, for example, Oculus Rift

Other methods

Pulfrich method

So-called " Pulfrich Glasses " with light / dark filters (eg " Nuoptix " ), use the " Pulfrich effect" for a 3D impression with lateral tracking shots and were, for example, by the RTL TV show Tutti Frutti early 1990 years very common. In the Pullfrich process it is not a true stereoscopic display, as the image is taken only with a single camera. The two perspectives for the left and right eye come about through the darkened lens, based on the Pulfrich principle. The darkened view is thereby passed to the brain with a time delay, so that two views from different perspectives (but staggered ) form the impression of space. This procedure is only very limited use, because here important conditions must be met in order for this method as a 3D method works at all. So the camera or objects must always (in principle and everlasting ) perform a constant, slow, only horizontal motion. If one of those conditions is not met, no 3D effect occurs.

ChromaDepth method

The ChromaDepth procedure of American Paper Optics is based on the fact that with a prism, colors are refracted to different degrees. The ChromaDepth glasses contain special view foils, which consist of microscopically small prisms. This light rays are deflected to different extents depending on the color. The light rays strike at different places in the eye. However, because the brain runs out of straight beams, gives the impression that the different colors were coming from different points of view. Therefore the brain generates from this differential spatial impression (3D - effect). The advantage of this method consists in the fact that you ChromaDepth images ( ie two-dimensional) can see fine without glasses - no annoying double images available. In addition ChromaDepth images can be rotated without loss of the 3D effect. However, the colors are limited only selected because they contain the depth information of the image. By changing the color of an object, then also its perceived distance changes. This means that a red object always in front, for example, green or blue will be objects.

Prism glasses glasses

A number of methods makes use of the effect of prisms to redirect the optical path. So, for example, uses the stereo - vision device SSG1b, also known under the name KMQ since the 1980s, this effect. Notably, books and posters, where it depends on color accuracy and simplicity. But it has been already used earlier in the screen or projection with few spectators. However, the user must maintain the appropriate distance to the image and hold his head permanently horizontal. Otherwise, the lines of sight of both eyes do not cover with the two sub-images, which are arranged among themselves. Hence also the English name of the method: Over- Under. These restrictions will be lifted in the future of an open hardware and open-source project openKMQ name for the computer work.

3D displays

Volume display

With a volume display physical mechanisms are used to represent points of light floating in space, eg via glowing voxels in gas, mist, or on a rapidly rotating ground glass disc or helix. Other solutions use several LCD.

One of the principles of a volumetric display is in fact the projection to move so that it sweeps out a whole volume. When this happens fast enough and depending on the position of the surface other contents are projected summarizes the human eye due to its inertia it all together in an overall closed 3D image.

One approach is the use of a spirally wound surface, shaped like a coil of an Archimedes screw. This surface is mounted and rotates about a vertical axis vertically. A 2-D projector projects a sector of the surface of the image, that is an inclined surface which is higher or lower depending on the actual total angle of rotation. The projector must be in sync with the rotation to that section projecting to the information that match the respective high points on the inclined surface. The Scottish television pioneer J. L. Baird announced in 1941 its volumetric 3D - and color TV system for a patent. Current laboratory systems (Japan, UK) using, inter alia, laser light sources.

Holography

A holographic 3D display reproduces the light field (or part thereof ) of the original scene.

Conclusion

The development of 3D displays include university, experimental and commercially available with different advantages and disadvantages in resolution, image quality, freedom of movement or prices and according to different application areas. Each technology has its limits and thus the appearance of flawless 3D images remains difficult.