Sharp DV-500D, Technical Manual

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DVD-Series
3-3 Moving Image Digital Compression Technology MPEG2
Enables Long Hour Reproduction
Even though the recording capacity of DVD discs is 7 times more than a CD, if a TV image on
NTSC is digitally transferred and recorded, even the DVD disc can record only 4 minutes.
Research of the technology to record more information in a limited recording capacity (data
compression) started in the 1960s. The progression has went from JPEG, MPEG1 to MPEG2.
MPEG1, which was adopted for Video CDs (karaoke, etc.), can record a maximum of 74 minutes
of moving images by compressing the data to 1/100, but the picture quality is inferior to LDs.
MPEG2 offers a high quality picture by compressing the information to approximately 1/40,
adding new technology to MPEG1 and increasing the compression rate. Diversified improvements
include changes in the data transfer rate (variable), frame rate (double) and predicting primenumbers
on corresponding pictures (double) between frames and field DCT.
Comparison of MPEG2 and MPEG1 pictures
Picture compression system
MPEG2(DVD) MPEG1(Video CD)
(adopted equipment)
Main picture degree 720 x 480 720 x 480
of resolution picture pixels picture pixels
Frame Rate
Data transfer speed 1~10Mbit/sec. (variable) 1.15Mbit/sec. (fix)
Average compression rate Approximately 1/40 Approximately 1/100
Picture quality More than LD About the same as VHS
*MPEG = Moving Picture Experts Group
This is the title of the compression technology working group, which is a part of the ISO/IEC
Joint Technology Committee, which in turn is part of the substructure of ISO and IEC.
1. Basic idea of MPEG 2
MPEG2 commands technological skill related to compression, which is comprised of about 20
items.
It increases the amount of information not only when complicated or fast moving pictures are
running (about 10Mbps),
but when slow or almost still pictures are running, it dramatically decreases the amount of
information (about 1Mbps).
Overall, it attains a high quality picture with a data transfer rate of average 3.5Mbps.
1/60sec.
60 pictures per 1 second
1/30sec.
30 pictures per 1 second