Cryptography Reference
In-Depth Information
test model. It aims to provide a common platform for different parties to
conduct experiments (core experiments) on their new technologies proposed
to the standard, so that the best technology can be adopted into the standard.
It also helps interested parties to get quickly familiarized to the standards.
There are two major international standard bodies working on creating
video coding standards. One of them is Video Coding Experts Group (VCEG)
under International Telecommunication Union Telecommunication (ITU-T),
and the other is The Moving Picture Experts Group (MPEG), a group formed
under the auspices of the the International Standards Organization (ISO) and
the International Electro-technical Commission (IEC). The MPEG committee
for video coding is formally named as ISO-IEC/JTC1/SC29/WG11.
MPEG has developed a number of video coding standards such as MPEG-
1/2/4, with applications mainly in entertainment industry and Internet
streaming. On the other hand, H.261/2/3 are developed by VCEG for appli-
cations mainly in communication industry such as video conferencing or video
telephony. Strictly speaking, H.26x are not international standards but only
recommendations of ITU-T. Recently MPEG and VCEG have been jointly
developed a new video coding standard called H.264/AVC, witch is a simpler
and much e
cient video coding system compared to its predecessors.
2.5.1 A Brief History of Video Compression Standard
The history of video compression can trace back as early as 1940s when the
analog television [17] was first designed, which used many elegant compression
techniques to reduce the signal bandwidth. For example, the use of interlaced
scanning has actually reduced half of the signal bandwidth compared to se-
quential scanning; the bandwidth of the color component is only one quarter
of that of the luminance; the two color difference signals are modulated on
two subcarrier which are of the same frequencies but orthogonal to each other;
the modulated color subcarrier is frequency interleaved with the luminance
signal so that it did not occupy extra bandwidth, etc.
The first digital video coding standards started in 1982 when the COST211
video codec, based on DPCM coding was standardized by CCITT (now called
ITU-T), under the H.120 standard. The H.120 codecs target bit rate is 2
Mbit/s for PAL system and 1.544 Mbit/s for NTSC system. However, the
video quality, although having very good spatial resolution, has a very poor
temporal quality. It was soon realized that in order to improve the picture
quality without exceeding the target bit rate, less than one bit should be
used to code each pixel. This is only possible if a group of pixels are coded
together, such that the bit per pixel is fractional. This led to the design of so-
called block-based video coding, and one of the first block-based video coding
standards is H.261.
