DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

4:2:0
(top field)
Y’ 0 Y’ 1
Y’ 2 Y’ 3
C B0–3
C R0–3
4:2:0
(bottom field)
Y’ 4 Y’ 5
Y’ 6 Y’ 7
C B4–7
C R4–7
Figure 40.3 Chroma
subsampling in fieldstructured
pictures
Film frame Top first field Repeat first field
A 0 0
B 0 1
C 1 0
D 1 1
Table 40.6 2-3 pulldown sequence in MPEG-2
Luma and chroma sampling structures
MPEG-2 accommodates 4:2:2 chroma subsampling,
suitable for studio applications, and 4:2:0 chroma
subsampling, suitable for video distribution. Unlike DV,
CB and CR sample pairs are spatially coincident. The
MPEG-2 standard includes 4:4:4 chroma format, but it
isn’t permitted in any defined profile, and so is unlikely
to be deployed.
There is no vertical subsampling in 4:2:2 – in this case,
subsampling and interlace do not interact. 4:2:2 chroma
for both frame-structured and field-structured pictures
is depicted in the third (Rec. 601) column of
Figure 10.1, on page 90.
4:2:0 chroma subsampling in a frame-structured picture
is depicted in the rightmost column of Figure 10.1; C B
and C R samples are centered vertically midway between
luma samples in the frame, and are cosited horizontally.
4:2:0 chroma subsampling in a field-structured picture
is depicted in Figure 40.3 in the margin. In the top
field, chroma samples are centered 1 ⁄4 of the way vertically
between a luma sample in the field and the luma
sample immediately below in the same field. (In this
example, C B0-3 is centered 1 ⁄4 of the way down from Y’ 0
to Y’ 2 .) In the bottom field, chroma samples are
centered 3 ⁄4 of the way vertically between a luma
sample in the field and the luma sample immediately
below in the same field. (In this example, C B4-7 is
centered 3 ⁄4 of the way down from Y’ 4 to Y’ 6 .) This
scheme centers chroma samples at the same locations
that they would take in a frame-structured picture;
however, alternate rows of chroma samples in the frame
are time-offset by half the frame time.
CHAPTER 40 MPEG-2 VIDEO COMPRESSION 479