Sharp DV-500D, Technical Manual

Page: 17 / 117

17
DVD-Series
(3) Coding
To record the quantitated numeric values more efficiently, they will be coded.
To make coding easier, the quantitated value of macro blocks will be scanned
in a zigzag pattern or alternately.
1
Ranlength Coding
Because there are a multitude of zeros (unnecessary information) in quantitated value,
it does not show all the zeros. What it shows, for example, is “six 0s” when there are 6
consecutive zeros.
2
Valuable length coding
Code is shown in binary numbers. Frequently showing numbers gets the shortest code,
and rarely appearing numbers get longer code in order to decrease the overall amount of
data.
4. Steps for Time Information Compression (Moving Picture)
Compression of moving pictures is done the same it is for still pictures.
Pictures are divided in macro blocks, and the movement changes on each block is “detected”,
“predicted” and “corrected”. Also, assuming there are many occasions when entire pictures will
be replaced by different ones, non-compressed original pictures (I picture) and less compressed
pictures (P picture) are inserted in frames at regular intervals. The pictures between them will
be inserted between these frames by predicting former and latter I and P pictures.
(1) Inserting original pictures between frame assumption
When an entire picture changes (random search, etc.), “detection”, “prediction” and
“correction” of the movement cannot be made.
Therefore, original pictures (intra = I picture) are inserted at intervals of every 6 to 15
frames and predicted pictures (P picture) from I picture every 2 to 6 frames.
Also, mutually predicted pictures among the I and P picture (bi-directionally = B picture)
are inserted between these I and P pictures.
B pictures (frames) on 1 ~ 2 below are predicted and made from I picture (frames) and P
pictures on 0 and 3.
0 1 2 3 4 5 6 14 15 16
B picture
intra
I picture
intra
I picture
Closeness to the
original picture P
Closeness to the
original picture P
B picture B picture
Example: Inserting I every 16 frames and P in every 3 frames.