Dolby 3D. Based on the movie "Avatar"

    Probably, many have already heard about the magnificent work of modern cinema called "Avatar". If you are not yet aware of this creation, then I want to draw your attention to some facts:
    • the creator of the film is the great James Cameron (Titanic, Terminator 1.2 - his work)
    • The script and ideas for the film appeared so long ago that before the start of work, people simply waited for the appearance of technologies that could realize what was conceived on the screen
    • the project was created for a long 14 years
    • budget paintings $ 237,000,000

    In my humble opinion, it turned out neither more nor less - a Masterpiece , which had not been there for a long time, and it is unlikely that within a few years something comparable in scale, beauty and depth will appear.

    However, everything would not be so bright and bewitching, if not for one of the technologies, which will be discussed in this topic.

    It is assumed that the reader already knows something about the methods of obtaining the effect of 3D images using anaglyph glasses of different colors, or glasses with an alternating shutter for each eye. If this is your first time encountering this, I recommend that you dig deeper into the matter using Wiki:

    Wikipedia - Stereo image
    Wikipedia - Anaglyph

    Dolby 3D

    Today, almost all new cinemas are equipped with this, at first glance, an intricate system for creating stereo images. What is it and why did ordinary anaglyphs disappear so quickly?
    In short, Dolby 3D is the commercial name for a system for creating a stereoscopic effect by mixing images with different wavelengths (Eng. "Stereoscopic visualization tool by wavelength multiplex imaging"), developed by the German company Infitec .
    The name Infitec comes from the words " In terference fi lter technology ", which actually reflects the main area of ​​research and development of this company - technologies related to the use of the interference effect (in this case, light waves). Initially, this 3D technology was created by Daimler Chrysler for virtual reality used in automotive design. In In 2006, Infitec teamed up with Dolby Laboratories to develop the Dolby 3D standard, which ultimately led the ordinary user to an interesting, affordable and exciting technology that allows you to more deeply immerse yourself in the atmosphere Yeru film or droplets without losing the beauty, quality and ease of viewing.

    Get to the point

    So, let's start in order. The light entering the human eye can be divided into three spectra comparable to the receiving receptors in blue, green, and red. The sensitivity of these receptors, depending on the wavelength, was measured by smart scientists, and they reflected the result of the work done in the form of such dependencies:

    Tricolor spectrum of human perception by different receptors
    Figure 1. Three-color spectrum of human perception by different receptors

    As you all probably guessed, specific receptors have specific and fairly accurate working ranges, beyond which their contribution to the creation of pictures in our minds tends to zero. In addition to this, the width of the emission spectrum, as a rule, is not critical, it only determines the degree of saturation of the primary color, however, even when using monochromatic laser emitters, it is possible to obtain a very saturated picture.
    Thus, in order to get a good color image, it is enough to use only three light sources with a very small spectral width of each of them:

    Spectrum of laser display
    Figure 2. Laser display spectrum

    When using such displays, one interesting possibility arises - the parallel transfer of image information in various triplets of primary colors. In order to transmit this information to the appropriate receiver (which in this case is the viewer's eye), the information must be filtered out by analogy with filtering the radio frequency signal using an oscillating circuit.
    Display spectrum and input filter characteristic
    Figure 3. Display spectrum (a) and input filter characteristic (b)

    At optical frequencies, the analogs of the oscillatory circuits are interference filters with a high figure of merit, made by the technology of deposition of thin layers of dielectric films on a transparent surface, such as glass. Physically, interference filters are paired resonators in which the number of resonators determines the selectivity of the filters.

    So what?

    Then everything is simple. Taking two triplets B1-G1-R1 and B2-G2-R2 and creating pairs of filters for the light source and for the receiver, we get two completely different images at the output when viewing them through different receiving filters (for the left and right eye).

    Create stereoscopic images using two color triplets
    Figure 4. Creating a stereoscopic image using two color triplets.

    The difference between the wavelengths of the same color for each eye can be up to 50 nm. This value is due to the good sensitivity of each receptor when deviating from their working maximum.

    Well, what about cinemas?

    The implementation of a film projector with two working triplets of colors is very delicate and prohibitively expensive, so the engineers created the device more simply. It can be used with projectors already installed.
    Dolby 3D spinning disk
    Figure 5. Dolby 3D system rotary disk

    The principle of operation of the disk is quite simple - it is placed between the projector and the screen, two half circles are filters for images of the left and right eyes, during operation it rotates at high speed to provide alternating switching of filter elements of different wavelengths . On each frame of the film, the disk rotates 3 times, that is, at a standard film frequency of 24 frames per second, the disk rotates at a speed of 3 * 24 * 60 = 4320 rpm.

    The disk is synchronized with the projector using a special device:

    Figure 6. Dolby 3D disk and projector synchronizer

    In addition to its direct function, this device has two buttons with which the disk can be either pushed into the projector’s work area or removed from it, which allows you to easily use the projector to show ordinary films without serious manipulation.
    Speaking of the projector ... Although it was not necessary to invent a completely new projection device, a replacement to the standard film projector is still required, because synchronization with the filter requires the same high frame rate, which means that it must update the picture per second with a frequency of as much as 6 * 24 = 144fps. These requirements are met by modern digital projectors, which are replaced by conventional film projectors. Currently, the main suppliers are NEC, Barco and Christie. All of them are built on 2K D-Cinema DLP technology (2K = 2048px x 1080px) and most of them use lamps with a color temperature of 6K. On the first 3D projectors, there was a problem of not turning DLP micromirrors as fast as possible , which led to incomplete illumination, and as a result, usually only 2/3 of the total flux of light hit the screen. Perhaps now the situation has improved.

    Glasses of the following shape are used as filter elements of the image receiver:

    Figure 7. Dolby 3D glasses

    Unfortunately, I don’t know anything remarkable about them, so let’s leave them as they are - glasses with deposited layers of an unknown dielectric :)

    The cost of the equipment is about $ 26,000, and the points are about $ 50.


    As you can see, everything is not as complicated as it seemed at first glance. The technology has been created, the bridgehead for conquering 3D worlds is open, the only thing left is to shoot a dozen more films similar to Avatar ...

    On this I want to finish my story, the basis for which was this document .

    Comments and additions are welcome.

    PS The article was written by my friend , who for some reason still does not have his own account on Habré. You can help him with this :) .
    Thank you for the invite hellt . The author of the Dipp article is now among us.

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