3d Videoconferencing - A New Option
It is a teleconferencing system that projects the image onto a mirror-based system and offers a three-dimensional appearance.
Thanks to information technology and communication can deliver a face as well as any image in real time. Pre-recorded images can be rotated and manipulated, and viewed in an arc of 360 degrees.
Motivation
Currently, a wide range of graphic content is modeled and rendered in 3D, although most continue to be represented in 2D drawings. Since 1908, the hand of Walter Lippman, had provided various forms of reproduction in 3D drawings, but only recent technological advances in digital capture, and computer screens have made the use of 3D displays is functional and practical. During a conversation face to face, eye contact and gaze direction provide important visual cues to express emotion, attention and interest, which the 2D video can not do. When a remote participant looks directly at the camera, everyone displays the video stream in the same way regardless of their position in space. Videoconferencing 3D point to multipoint get an exact reproduction of the direction of gaze and eye contact.
To carry out this communication, the system must have a number of fundamental requirements:
Display emitting rays of light in 360 degrees with proper horizontal parallax.
Face detection system to produce a correct vertical parallax.
Software and hardware capable of processing data in real time.
Algorithm capable of rendering different centers of projection of a surface OpenGL anisotropic with a correct vertical perspective to any user at any point.
The participant appears in natural size and in correct perspective for eye contact. The participant looks at the audience through a 2D video while being scanned, transmitted and rendered at high speed.
Technology
The system is based on a display consisting of several elements:
A high-speed DLP projector
Two rotating mirrors coated with a holographic diffuser.
A synchronization engine.
A standard PC.
The image of the room reflected in these mirrors, rotating them quickly enough, you get to project an image 360 degrees. With proper synchronization, you can display images for the left eye and right eye slightly different, and make an image appear in 3D.
High-speed projector
To achieve a high rate of frames per second, the system plays each of the 24 bits that make up a color image in separate frames sequentially in separate frames. Thus, if the digital video input is 60Hz, the projector reproduces 60 x 24 = 1.440 frames per second. To achieve the optimum rate for the system, is set to a frequency of 200Hz, using two DLP projectors, and can thus achieving up to 8640 frames per second video signal using a DVI specially encoded.
Rotating mirrors
The display works by projecting high-speed video projector that comes in a rotating mirror system. As the mirror rotates, reflects a different image and accurately to each viewer. The size, geometry and material of the rotation surface have been optimized for displaying a picture of the size of a human face. His way of two passes provides two sides of the display surface for each viewer in a complete rotation, getting a visual upgrade from 30 Hz to 900 rpm. Indeed, the mirror reflects 144 unique views of the scene through a field of view of 180 degrees with an angular separation of 1.25 degrees.
Motor synchronization
The surface of the mirror rotates synchronously with the images are being reproduced by the projector, the rate used as masters of information coming from the PC signal. The FPGA projector decodes each of the frames and communicates directly to the sync engine. Since the frequency with which the mirror is rotated 30 times per second, the human visual system captures the light, recreating an image of an object or person floating in the center of the mirror.
Real-time 3D scanning
The system uses a monochrome camera to capture the face of the remote participant to a minimum frequency of 120 Hz and high-speed projector calibration at that frequency (the same as using the camera).
Another possibility for the system is to compute the depth maps of the face of the person. For this, two images are acquired for each frame, and light the opposite way.
Then subtract the two images to detect zero crossings and get the absolute position of 3D pixels from the center of the face. Conveniently, the top half of the two images illuminated texture map provides a fully illuminated for the face, while the minimum value approaching us the amount of ambient light in the scene.
The result is a depth map for face, we pass along with the facial texture maps.
Face detection for vertical parallax
To provide accurate distance and eye contact, the rendered image of the remote participant must seem entirely consistent with the space coordinates seen by anyone in the audience. Render face the same height and distance to the public can make it appear that the image is facing a very precise angle for some people, although the horizontal parallax provided by the display is generally accurate in the horizontal direction. Although the vertical sensitivity with less sensitivity to detect the horizontal, a real sense of eye contact requires both. To correct the vertical perspective, markers are used OpenCV face detection based on Viola-Jones detector, and a Kalman filter to reduce the additive white noise, to track the delivery approaches based on 2D video. Thus, the parallel horizontal display provides a binocular stereo image without any delay, while the vertical parallelism is achieved through monitoring.
Types of display surfaces
The surface of a display provides information about how they will behave the emitted light toward the audience. Flat surfaces and concave / convex can be used. These surfaces in different ways offer different advantages and disadvantages, which shows the usefulness of being able to project images on arbitrary surfaces.
Flatbed: It has a steep angle to better match the shape of a face and two sides for double the frame rate of the screen.
The projector beam diverges horizontally divergence after reflection by the surface of the flat screen, so that about an area of about 20 degrees of hearing, looks at some pixels reflected the projector in any position of the mirror. On the other hand, is the simplest to build and calibrate although other forms may provide more useful optical properties.
Concave surface: The utility of this surface is that at any time, any member of the audience can see the light reflected from the projector. This type of surface is useful for the detection of the spectators. The display can render the proper vertical perspective for each viewer in a direct manner with a single variation in height and distance chart. Different forms also affect the focal length of display. The focal area for an audience is composed of different layers of the mirror illuminate when the mirror rotates. For a plane mirror, the focal surface is a cone centered around the axis of the mirror. Concave and convex surfaces are asymmetric focal may change depending on viewing angle.
Convex mirrors produce a set of focal planes concave, and concave mirrors produce a convex set of focal planes. This is another advantage in the concave mirrors, as the human face is more like a cylinder with a convex concave. When the focal surface is approaching the object is playing, visual accommodation is more accurate and minimizes aliasing.
Beyond the reflective surfaces are expected to display auto-stereoscopic capabilities have a decisive impact on 3D communication applications. These displays based on LCD technology along with the use of optical diffraction barrier or have demonstrated to show different images depending on the angle at which you look at the screen. This addition allowed to see 3D without glasses, teaching also allows different perspectives of a scene depending on the angle at which you look at the screen. 3DPresence FP7 European project has built what is the first working prototype with this technology.
Future
In general, these systems aim at the progressive improvement of the quality of image and communication. The color may be achieved by placing multiple synchronized projectors in the same beam. The gray level reproduction may be enhanced by incorporating advanced halftoning algorithms, but should be optimized to work at thousands of frames per second.
On the other hand, is a disadvantage that the remote participant can not receive a 3D vision of the hearing which establishes communication, although the display is positioned and calibrated to optimally estimate the current position of each person. Replace the screen of the remote participant 2D for autostereoscopic monitor solves the case as demonstrated in the European project FP7 3DPresence. The following video includes images of the system developed 3D TelePresence Presentation 3DPresence
In conclusion, a 3D video system provides a significant step in the human face to face communication at a distance.
by: Ronald Newman
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