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Video primer: HDR, 3D processing challenges

Posted: 05 Jul 2011 ?? ?Print Version ?Bookmark and Share

Keywords:video processing? 3D? video systems?

In response to consumers' incessant demands for video content of even higher resolutions, the standards bodies ISO/IEC and ITU-T have identified the need for a new video coding standard that further improve compression efficiency to enable the transmission and storage of high resolution content. The Joint Collaborative Team-Video Coding (JCT-VC) was formed to coordinate the "high-efficiency video coding" (HEVC) effort of realizing a video coding standard able to provide a 50 percent reduction in the required video coding bitrate, in relation to H.264/AVC. The inaugural meeting was held in April 2010, with I2R's involvement highlighting a keen desire to pervasively contribute to this initiative.

In this report
??HDR, 3D challenges
??Compressing HDR, 3D videos
??HDR, 3D video display
??Searching for video content

For HDR videos, compression can be achieved by increasing the precision of input pixels. Traditionally, video compression techniques have considered only 8bits-per-pixel (bpp) input videos, yet HDR videos require 10C14bpp. Consequently, the H.264/AVC standard was amended to allow for the input of HDR videos of up to 14bpp. The HEVC standard currently being designed is also expected to provide the necessary capabilities to handle HDR videos of up to 14bpp.

In the 3D realm, however, the choice of compression technique hinges on the way these videos are represented. Of these, one approach represents a 3D video as a collection of multiple 2D views, as how a stereoscopic video consists of the left and right view. Here, an apparent compression scheme involves independently compressing each view in an approach known as "simulcast." Nevertheless, significant overlap might exist between these views, and the amount of redundancy contained within can be exploited for further compression.

The Pulfrich effect
The Pulfrich effect is a psychophysical percept where an illusion of depth is produced by introducing differences in the times at which a moving object is presented to the two eyes.

In the classic Pulfrich effect demonstration, a subject views a pendulum swinging in a plane perpendicular to the observer's line of sight. When a darkened lens, typically gray, is placed in front of the right eye, the pendulum seems to take on an elliptical orbit and appears closer as it swings toward the right and farther as it swings toward the left. If it were to be viewed from above, it would look like the pendulum was revolving counterclockwise. More on the Pulfrich effect.

HDR, 3D video display
Most existing display devices can already display HD videos, but technologies for 3D and HDR videos have not enjoyed similar successes despite the increasing availability of 3D television sets in the market. In HDR technology, the gap between the dynamic ranges of display devices and that of real scenes prevent the display of such videos using existing monitors. Other than attempting to preserve the "feel" of the scenes while compressing the dynamic range of HDR videos, devices can be designed to directly represent HDR videos. As in the case of HDR capture technologies, the foreseeable future will correspondingly witness the emergence of HDR monitors, printers and other output devices.

For 3D videos, however, it is imperative to note that their displays involve projecting stereoscopic images separately to each eye. To this end, two strategies have been adopted. First, 3D glasses are used to project the offset images to the respective eyes. For example, anaglyphic 3D uses passive red-cyan lenses while polarization 3D employs the use of passive polarized lenses. Second, instead of the user having to wear glasses, the display device itself assumes the responsibility of projecting the appropriate stereoscopic images into the viewer's eyes in a display technology termed auto-stereoscopy.

Additionally, while single-view displays project only one stereo pair at a time, multiview displays exploit the use of head tracking devices to change the view depending on the viewer's head position and viewing angle. In the special case of auto-multiscopic displays, multiple independent views of a scene are projected to a number of viewers. These views are created instantly using the above-mentioned "2D views with depth information" approach. Various other display techniques such as holography, volumetric display and the Pulfrich effect also exist.

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