X2

304 MPEG glossary
to frame. A large count does not make much sense, since GOP has a maximum length of
1
n
I
r
belongs to the next GOP.
I
Intra-frames: In these pictures, the entire image information of a frame is saved and only
information from this frame
B
f
"
I
For historical reasons, pictures in a movie are always recorded and transmitted in the form
o
f
the processing of the TV tube puts the two frames together to form one.
5 (4P, 2B) in PAL and 18 (5P, 2B) in NTSC. (More than 2 B frames between P frames is
ot allowed).
n a
closed GOP, B frames of the last subgroup may contain only backward predictions or
eferences to the preceding P frame, but no references to the following I frame, since it
frames
is used ("intra-frame encoded"). In contrast to the I frame, P and
frames save only the differences between the current frame, and preceding and/or
ollowing frame are also found in MPEG video (P frame = "predicted frame", B frame =
bidirectional frame", see
Prediction (view page 305)).
nterlace
f two fields; first the lines with even numbers and then those with odd numbers. These
ields are alternatively displayed with double the frame rate. The (lazy) eye of the viewer or
T
Y
the entire processing chain as fields and is exported again as fields or burned onto DVD or
shown on TV when played back on a DVD as a full picture. Only in certain rare conditions is
it necessary to go deeper into this process. Two problems can occur:
1
T
a
T
between whic
a
he output image First field Second field
ou normally don’t have to worry about field processing. The video material goes through
. Interlace artifacts
o be displayed on a computer monitor (during recording, in your TV/VCR, and in the
rranger during editing), the two fields must be combined to form a full screen.
hese two fields are not the same, since two fields are created during the recording
h a 1/50 of a second gap is evident. Moving objects can therefore produce
rtifacts on vertical edges.