DV-560H (serv.man6). DVD Technical Manual (Based on the DV560H) - Sharp DVD Service Manual (repair manual). Page 8

Decreasing the thickness of a disc can cause less focus movement against similar disc inclination
and less focus disorder.

Even by making the track longer and the pit smaller to expand capacity, it is not possible to
record one whole movie on one side (1 layer) of a 12cm DVD disc if using current image data
information.  To reproduce 133 minutes on a 1 layer on 1 side disc, it is necessary to digitally
compress the image data.
Most digital compression technology of data is done is the audio field.
It is already routinely used in personal computers and MD.
To make comparisons with the audio field, digital compression technology for images, which
contain far more information, were processed by the MPEG (Moving Picture Image Coding
Expert Group) committee of ISO, and became the world standard.
First, MPEG1 (a fixed bit rate system) was standardized and made practical for use in video CDs
(karaoke, etc.).
Then, MPEG2, DVD actualization, became standardized.  MPEG2 is called “Variable Bit Rate
System”.
It compresses information while changing the amount of data, depending on the amount of data
on the image.  That means, it compares the former and latter images, then records the amount
of change as data.

The image performance of DVD actualizes 500 horizontal lines of resolution, an increase from
traditional recording media.
Currently, it is superior to the “the media with the highest quality image”, an LD (430 horizontal
lines of resolution).  It matches master tapes made to professional specifications.
With its high quality imaging and high number of resolution lines, image outlines are sharp.
Even in dark scenes, there is less noise and clearer perspective.

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