User manual

MPEG glossary 131
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I frames
Intra-frames: In these pictures, the entire image information of a
frame is saved and only information from this frame is used
("intra-frame encoded"). In contrast to the I frame, P and B frames
save only the differences between the current frame, and preceding
and/or following frame are also found in MPEG video (P frame =
"predicted frame", B frame = "bidirectional frame", see Prediction
(view page 133)).
Interlace
For historical reasons, pictures in a movie are always recorded and
transmitted in the form of two fields; first the lines with even numbers
and then those with odd numbers. These fields are alternatively
displayed with double the frame rate. The (lazy) eye of the viewer or
the processing of the TV tube puts the two frames together to form
one.
The output image First field Second field
You normally don’t have to worry about field processing. The video
material goes through 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. Interlace artifacts
To be displayed on a computer monitor (during recording, in your
TV/VCR, and in the arranger during editing), the two fields must be
combined to form a full screen.
These two fields are not the same, since two fields are created during
the recording between which a 1/50 of a second gap is evident.
Moving objects can therefore produce artifacts on vertical edges.