DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Frame 0 Frame 1
Y’ 0 Y’ 1 Y’ 0 Y’ 1
Y’ 2 Y’ 3 Y’ 2 Y’ 3
C B0–3
C R0–3
C B0–3
C R0–3
Figure 11.7 Chroma subsampling
in 4:2:0p alternates
frame-to-frame in a twoframe
sequence, even though
scanning is progressive.
Quasi-interlace in consumer SDTV is
comparable to progressive
segmented-frame (PsF) in HDTV,
though at 25 or 29.97 frames per
second instead of 24. See page 62.
sampling rate of 18 MHz (i.e., 4 ⁄3 times 13.5 MHz). This
scheme offers somewhat increased pixel count
compared to 4:3 systems; however, it is rarely used.
Progressive SDTV (480p/483p)
A progressive 483p59.94 studio standard has been
established in SMPTE 293M, with parameters similar to
Rec. 601, but without interlace and with twice the data
rate. Some people consider 483p to provide high definition.
Unquestionably, 483p has higher quality than
480i, but I cannot characterize 483p as HDTV. Japan’s
EDTV-II broadcast system is based upon 483p scanning.
Provisions are made for 480p in the ATSC standards
for digital television. One major U.S. network has
broadcast in 480p29.97, one of the ATSC formats.
480p and 483p systems have either 4:2:2 or 4:2:0
chroma subsampling. The 4:2:2p variant is a straightforward
extension of Rec. 601 subsampling to progressive
scanning. The 4:2:0 variant differs from 4:2:0 used in
JPEG/JFIF, and differs from 4:2:0 used in MPEG-2. This
scheme is denoted 4:2:0p. Unfortunately, this notation
appears to follow the naming convention of MPEG-2’s
4:2:2 profile (denoted 422P); however, in 4:2:0p, the p
is for progressive, not profile!
Figure 11.7 depicts 4:2:0p chroma subsampling used in
483p. Although frames are progressive, chroma
subsampling is not identical in every frame. Frames are
denoted 0 and 1 in an alternating sequence. Chroma
samples in frame 0 are positioned vertically coincident
with even-numbered image rows; chroma samples in
frame 1 are cosited with odd-numbered image rows.
Compare this sketch with Figure 10.1, on page 90.
Some recent cameras implement a progressive mode –
in DVC camcorders, sometimes called movie mode, or
frame mode – whereby images are captured at
480p29.97 (720×480) or 576p25 (720×576). The DV
compression algorithm detects no motion between the
fields, so compression effectively operates on progressive
frames. Interlace is imposed at the analog interface;
this is sometimes called quasi-interlace. Excellent
stillframes result; however, motion portrayal suffers.
100 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES