Cryptography Reference
In-Depth Information
bit rate allowed, MPEG-1 has not only to eliminate redundancy but also to
eliminate a fair amount of information as well. The source entropy is reduced
by sub-sampling in all three dimensions.
The following steps show an example of how an ITU R-601, 4:2:2 PAL
component video input can be converted to a format that is suitable for storage
in Video CD using MPEG-1 video coding,
• Discarding every other field. This results in a progressive scan system
with a frame rate of 25 or 30 Hz. It also halves the data rate and neatly
circumvents interlace handling. It halves the vertical resolution of the video
frames.
• The horizontal resolution is halved by sub-sampling to 352 luminance pix-
els per line.
• The chroma signals are sub-sampled horizontally so that there are 176
pixels per line.
• The chroma signals are also sub-sampled vertically so that on alternate
lines there are no chroma pixels. This is so-called 2:1:0 coding. This pre-
processing produces what is known as the Source Input Format (SIF).
Beside reducing the resolution, discarding every other field damages the
motion portrayal ability of the system and makes it the same as the motion
picture film. Thus the common claim that MPEG-1 offers VHS quality is not
really true.
2.5.4 MPEG-2
Following the success of MPEG-1, MPEG-2 [20] aims to provide a generic cod-
ing method for high quality moving pictures and associated audio. The target
applications are CCIR 601 TV and HDTV. The MPEG-2 core algorithm is
still a hybrid DCT/motion compensation scheme which is backward compat-
ible to MPEG-1 and can be considered as the superset of MPEG-1. This is
the first joint work between MPEG and VCEG. Therefore MPEG-2 can also
be called as H.262. Similar to MPEG-1, MPEG-2 has achieved tremendous
success in the application of digital versatile disk (DVD) and digital television
broadcasting.
In order to support a diverse range of applications, MPEG-2 integrated
many different algorithmic tools into the full standard. To implement all the
features of the standard in all decoders is unnecessarily complex and costly,
so a small number of subsets of the full standard, known as profiles and levels,
have been defined. Besides the profiles and levels, MPEG-2 introduced a num-
ber of other extension compared to MPEG-1, those include interlaced coding,
different zigzag scan patterns, and spatial, temporal and SNR scalability, etc.
MPEG-2 Profiles and Levels
MPEG-2 is designed to support a wide range of applications and services of
varying bit rate, resolution, and quality. MPEG-2 standard defines 4 profiles
