DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Component 4:2:2
Rec. 601-5
The technique of Figure 11.6 is
used on many widescreen DVDs.
A DVD player can be configured
to subsample vertically by a factor
of 3 ⁄ 4 , to letterbox such a recorded
image for 4:3 display. (Some DVDs
are recorded letterboxed.)
525
480i29.97 WIDESCREEN 576i25 WIDESCREEN
483
858
720
13.5 MHz 16:9
Widescreen (16:9) SDTV
Television programming has historically been produced
in 4:3 aspect ratio. However, wide aspect ratio
programming – originated on film, HDTV, or widescreen
SDTV – is now economically important. Also,
there is increasing consumer interest in widescreen
programming. Consumers dislike the blank areas of the
display that result from letterboxing. Consequently,
SDTV standards are being adapted to handle 16:9
aspect ratio. Techniques to accomplish this are known
as widescreen SDTV. That term is misleading, though:
Because there is no increase in pixel count, a so-called
widescreen SDTV picture cannot be viewed with
a picture angle substantially wider than regular (4:3)
SDTV. (See page 43.) So widescreen SDTV does not
deliver HDTV’s major promise – that of dramatically
wider viewing angle – and a more accurate term would
be wide aspect ratio SDTV.
The latest revision (-5) of Rec. 601 standardizes an
approach to widescreen SDTV sketched in Figure 11.6
above. The standard 13.5 MHz luma sampling rate for
480i or 576i component video is used, but for an
image at 16:9 aspect ratio. Each sample is stretched
horizontally by a ratio of 4 ⁄3 compared to the 4:3 aspect
ratio of video. Existing 480i or 576i component video
infrastructure can be used directly. (Some camcorders
can be equipped with anamorphic lenses to produce
this form of widescreen SDTV through optical means.)
A second approach, not sketched here, uses a higher
CHAPTER 11 INTRODUCTION TO COMPONENT SDTV 99
625
576
864
720
13.5 MHz 16:9
Figure 11.6 Widescreen SDTV sampling uses the standard
13.5 MHz sampling rate, effectively stretching samples horizontally
by 4 ⁄3 compared to the 4:3 aspect ratio base standard.