X2

MPEG glossary 303
b
- Y, V = G -Y).
T
brightness and color information to be handled separately. The first data reduction occurs
w
r
o
reading.
4
t
data.
4
F
This corresponds to a output data compression of 1/2.
F
A
p
F
A
for example, contains 25 frames per second, NTSC 29.97 frames.
V
f
i
compression are based on such frames. Video editing literature usually refers to frames.
GOP
G p of Pictures: The sequence of I frames and the P and B frames that belong to them.
e
rightness value (Y = 0.299*R = 0.587*G + 0.114*B) and two color difference values (U = R
he Y value alone produces the black and white picture. These signal components allow
hen single rows comprising a picture are read. Because the human eye has a lower color
esolution than a brightness resolution, the color components are recorded only for every
ther point of a row (4:2:2) for each four pixels grouped (4:1:0), i.e. color signal under-
:2:2 This corresponds to the established TV standard. One piece of color information is
ransmitted per row for two pixels which corresponds to a 2/3 compression of the output
:1:0 This is the color coding used for DVDs and most other consumer video applications.
or each 4 pixels grouped together on two rows, one unit of color information is saved.
ield
half-image, i.e. two halves which combine to produce a frame (see de-interlacing (view
age 304)).
rame
frame is a single image from a video sequence which also called a full image. PAL video,
ideo recordings, with the exception of computer animations and still frames, don't contain
ull images. Instead, they have double numbers of half-images (fields) which are transmitted
n an interlaced state. However, we still refer to frames, since many predecessors of MPEG
rou
.g. I B B P B B P B B I ...
(This GOP has a length of 9, with 2 P frames and 2 B frames)
I
i
m
T
I
synchronized. Between the I frames only a limited count of P and B frames is allowed. This
e
d
frames contain the entire image information of a frame, while P and B have part of the
nformation. So-called prediction (view page 305) and movement approximation are
ethods used for reduction.
he combination P B B is called a subgroup.
frames must appear in regular intervals in the data stream for image and sound to be
xplains a few things: Since P and B frames contain only differential information, these
ifferences will be larger with time, since more and more changes takes place from frame