Active and passive 3D methods of obtaining three-dimensional image

Binocular (stereoscopic) vision allows us to perceive the world surround. Of course, he is the main problem for 3D TV or 3D projector in the theater is that the show with this surround the world need to flat screen.

three-dimensional world on a flat screen

If You have forgotten how our brain forms a 3D image, and want to learn the secrets and ways of the first volumetric display on flat surfaces, I recommend to start with the first part of this article: 3D-format, three-dimensional image (part 1), otherwise, some portion of material presented here, it might seem strange ab

As we already know, in order to watch on TV or in the cinema videos in 3D, you need at least to have two images: one for each eye. This can be achieved in various ways, let's look at each of them and let's start with the so-called passive 3D, because the passive 3D more than active

  • Anaglyph method:
  • This is perhaps one of the oldest ways of getting 3D effect, however, due to its simplicity, use it now. Anaglyph images are created by using color filters to remove a portion of the visible spectrum of the images intended for each eye: red channel has an image for the left eye, and blue - for the left

    Anaglyph method

    for Anaglyph glasses, to view these images you can make one yourself using blue and red filter (purple green), but you can buy ready-made. These glasses usually come to Chinese portable "3D-TV" (cots)

    Anaglyph glasses

    The original image is recorded two (ideally) or one (if you have any further digital processing of the material) cameras located at different angles, each of which is equipped with a filter. When viewing, it is only one source (although there may be two) each eye sees only the image intended for it, since the second - cut off filter

    Filters and receive volume

    Advantage anaglyphic method is that no special display, you do not need any standard 2D display (planar) or a TV capable of outputting anaglyph three-dimensional image, and make points easy at home.

    Drawback is a disgusting color, because a large part of the color gamut will be clipped or distorted color filters, and our brain, in contrast to the electronic circuits of the TV, unable to "recreate" green color, having, as information, only blue and red. As a consequence - fatigue eye discomfort and headache, so advised not to get involved in this way of viewing dn

  • Methods of polarization: linear polarization
  • In 1932 year Edwin Land (founder of Polaroid) starts production of polarizing film, which plans to use sunglasses to suppress the sunshine (sunglasses on this technology, by the way, are still issued). For the first time viewers get to watch a normal, full-color stereoscopic (or stereo) image, however, it is not all went smoothly

    Methods of polarization

    The principle of linear polarization is very simple (it is also used in LCD and LED televisions): the light passing through such film, "ball" becomes a flat "pancake" (as if "forced" through the form with horizontal or vertical cuts)

    Survey and demonstration was performed by two synchronized cameras. Lenses in transmission cameras (in theaters) was polarized: one is vertically and the second horizontally (or "diagonally", but also at an angle of 90 degrees). Glasses, for viewing 3D movies, were polarized: one glass horizontally, the second vertically. Screen, to demonstrate stereo movies, had a special metallic coating (they were called "silver"), which was able to reflect the incident polarized light from both cameras without changing the direction of polarization (with no diffusion)

    Linear polarization

    The light reflected by the screen, polarized horizontally, could "pass" only through the glass of points, which were polarized in the same horizontally and couldn't get through the second, vertically polarized, that is, the image was only seen one eye. For the second eyes intended image with the second camera, with vertical polarization, the result is each eye saw only the image that was intended for him.

    Advantage this method is the lack of flicker, as both images are displayed simultaneously, if you remove the glasses, it's just "blur", but no flickering and good, correct color (in the 80's I watched a 3D movie in the cinema ab )
    Disadvantages: his head had to keep straight and be center of the screen, or change mutual angle between the directions of polarization camera and glasses, which led to the loss of 3D stereo effect and distorted the picture, it was difficult to synchronize two different cameras (don't forget that the cameras were analog, and the movies were recorded on film)

    the Principle of linear polarization

    Later, began to use one digital camera and a filter, switchable polarization. In this system, image frames, for left and right eyes are displayed sequentially one after the other. The electronic filter is synchronized with the camera, could change the direction of polarization of the light flux from the camera, so all the same "silver" was displayed consistently frames with different polarization for each eye. The main drawback - unpleasant to the eye flicker, as a time when the left eye "sees" the picture, the right sees nothing (for him, at this time, complete darkness) and Vice versa

  • Methods polarization: circular polarization
  • The issue of restricting the viewing angle (head tilt) was able to solve by resorting to the method of circular polarization (by the way, the famous "Avatar" movie I have seen in 3D cinemas equipped with this equipment and points ad ). When circular polarization filtering is performed depending on the rotation direction of the polarization vector in the plane perpendicular to the direction of wave propagation (left and right rotation):

    Circular polarizationLeft and right rotation

    Everything else is similar to the method of linear polarization: wearing glasses, each eye sees only the image that is polarized in the same direction (left or right), and glass points. Uses one digital camera and electronically-switchable filter. Color reproduction and 3D effects do not disappear when tilting the head or viewing at a slight angle to the screen. This method is suitable not only for viewing 3D movies in cinemas, but for the LCD monitors and televisions.

    Glasses circular polarized

    3D display can be manufactured with polarization filters, which are superimposed on the lines of the display pixel or to have already polarized lines (rows) of pixels. Then one "group" (row) of pixels will give us the picture for one eye (all in the same glasses, of course) and the other for the second. To play back stereoscopic 3D videos, for example, Blu-ray 3D on a polarized display, the right and left video frames will be converted to interlaced. The display will show the even lines for one eye and odd for the other. What can we lose? - half the screen resolution, than the face? - move the picture up and down on the monitor and watch her eyes (blue and red lines on it to symbolize the even and odd lines):

    Interlaced format

    Let's summarize. To benefits 3D-format, by circular polarization include relatively low equipment cost, good color rendition and absence of flicker (LCD panel) disadvantages - a loss of half the screen resolution (in display units) or flickering (in theaters), the polarizers absorb half brightness of the original image, blurring image edges and fine details

  • Packing technology:
  • So far we have considered passive 3D technology, now it's your turn to tell you about active 3D technology or simply 3D. The history of this technology takes us to the distant 1922 year when Laurens Hammond is its system for watching movies in stereo format: Teleview. Two projectors were sent to the canvas frames alternately. Next to each audience stood a special device, mounted in the armrests of chairs - "visor". Inside the round box "shield" rotates the disk, something resembling a bow tie, and the bottom had two holes for eyes, through which you could see the screen

    Lawrence Hammond and format Teleview

    If everything is synchronized accurately, then the blinds closed the screen for the left eye, leaving the visibility to the right, and Vice versa, in accordance with the staff. The problem was that to achieve a stable synchronization of such number of mechanical devices is not easy, and the quality of the "original image" left much to be desired ac

    Curtains & sync

    A return to this technology occurred only in the early 21 century, when, with the development of LCD displays has become possible to manufacture the 3D glasses with paddles, spring 2010 of the year already in many stores sold 3D TVs equipped with a pair of these glasses. Packing technology and liked the cinema, which, abandoning the polarized 3D glasses, went to the slide.

    Shutter method 3D

    3D glasses with active shutters are two LCD matrix (for more information about working principle of LCD display read here: LCD TVs) that are controlled by infrared rays from the synchronizer. Each of the matrices (left and right glass) can be in two States: open and closed. If the matrix is "open", the light passes freely through it and the eye "sees", if "closed" then the light cannot pass through it and the eye will not see anything (this glass will be just "black").

    According to the control signal coming from the sensor on the TV or on a movie screen, glass-matrix points alternately switched: one glass is closed and the second open. The projector or TV at this time, send your screen independent images intended for each eye. Thus, in each moment, we actually see one image with one eye, and then, because of the inertia of our eyes, and our great processor - the brain is a "formation" full volumetric images ab

    3D glasses with active shutters

    In order to reduce flicker to the minimum required to transmit frames with a frequency of at least 60Hz, and given the fact that our "skull" still need to stitch the two frames are obtained for left and right eyes, get 120Hz. Projector is not a problem, but for TV or monitor with HD resolution... is not very good bn

    In addition, the difficulty arises with the delivery of Full HD 3D signal from the source to the TV. Firstly, must be read from disk by two-channel system, and then another, and to transmit a signal, and to transfer will need HDMI 1.4, because today common interface HDMI 1.3 may not cope with the transfer of 120 fps as a Full HD

    Camera 3D shutter technology

    Now available for home viewing 3D glasses supplied NVIDIA 3D Vision to view a 3D image on the screen of the PC monitor, TV or laptop-book", just remember that this system can only be connected to monitors that support high definition resolution (HDTV 1080p)

    NVIDIA 3D Vision

    Advantages of the active shutter 3D technology: excellent color rendition, clear image, wide angle viewing with no loss of quality 3D movies on the monitor or TV at full resolution (recall that in the method of polarization You see with each eye only half of the full resolution of the screen)
    Disadvantages: expensive glasses, which require power from the battery or the battery in the sync issues - double vision, loss of brightness due to the incomplete transparency of the lenses of matrices of 3D glasses (loss of brightness with polarized glasses - less)

  • Shutter or polarization?:
  • Now, technology polarization and gate, is actively vying proving to us that each of them is best, however, the best way to check this is to see with your own eyes, not on billboards, and "live", as a considerable part of the advertising true, here is one example: firm LG argued that their monitors based on polarization technology, in front of others, using the page flipping method.

    First, not as the "gate" falls brightness, as shown in the advertisement, and secondly, the butterfly is not fly the boundaries of the screen (about this and other "jokes", read in the third part of the article) and finally - why the display size is different? dq

    Image outside of screen

    Looking further, we show that we will see the image with both eyes simultaneously, but mentions that each eye sees only half permissions (through-line scan to form two channels of the image), and when the packing is full resolution, but half the time bk

    Comparison of technologies

    But I can argue what technology will be less doubling, will provide the best clarity and color reproduction, and the main - less fatigue for the eyes bt

    Shutter or polarization?
  • 3D format and our health:
  • We argue that viewing 3D movies non-hazardous to health and eyes nothing to fear? Then why do they start ache or actually "diverge" after watching, especially on the big screen be Where you may receive the headache? Say it's of "flicker", however, there is much more good reasons that pose a danger to our health, not only physical but also mental bm

    Read more: Dangerous! 3D and unreal volume

    Link to this story: http://en.rem-tv.net/publ/3-1-0-57

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