Sony D8MM-01, Training Manual

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19
The following explains the compression process as the 1999 D8 models
use it. Each IC’s purpose is examined to provide you with a better under-
standing of the whole process.
IC351 VFD
Video Encode
IC351 also contains a NTSC encoder so that it may send composite sig-
nals to the IR Out and Video Out, and component video to the viewfinder
and LCD if applicable.
Blocking
§
The first step in bit reduction is taken here by eliminating portions of
the frame that cannot be seen. This is done by removing the data
that cannot be seen from the outside edges of the picture. This re-
duces the number of bits from 162Mbps to 127Mbps.
Shuffling
Shuffling is a technique used to keep the activity level of the compression
circuit relatively smooth. The macro blocks are divided into ten bands.
Note: There are ten sub tracks of video in one frame. Shuffling works
by building the compression blocks out of macro blocks that are not adja-
cent to each other. While shuffling may randomize the data, it does oper-
ate on a preprogrammed equation. This is so the data can be de-shuffled
before recording.
·
The frame would be 720 pixels by 480 pixels after the unseen picture
information is eliminated. This is then broken down into 8 pixels by 8
pixels segments called DCT blocks. These blocks are then combined
into Macro blocks. One Macro block consists of four DCT blocks of Y
and one DCT block each of the color difference signals, Cb and Cr.
Consequently a macro block is made up of a total of six DCT blocks.
Later, we will see that five Macro blocks make up one compression
unit.
Blocking
Shuffling