DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

By NTSC and PAL, I do not
mean 480i and 576i, or
525/59.94 and 625/50!
When I use the term PAL in this
chapter, I refer only to 576i
PAL-B/G/H/I. Variants of PAL
used for broadcasting in South
America are discussed in Analog
NTSC and PAL broadcast standards,
on page 571. PAL variants
in consumer devices are
discussed in Consumer analog
NTSC and PAL, on page 579.
Composite NTSC or PAL encoding has three major
disadvantages. First, encoding introduces some degree
of mutual interference between luma and chroma.
Once a signal has been encoded into composite form,
the NTSC or PAL footprint is imposed: Cross-luma and
cross-color errors are irreversibly impressed on the
signal. Second, it is impossible to directly perform many
processing operations in the composite domain; even to
reposition or resize a picture requires decoding,
processing, and reencoding. Third, digital compression
techniques such as JPEG and MPEG cannot be directly
applied to composite signals, and the artifacts of NTSC
and PAL encoding are destructive to MPEG encoding.
The bandwidth to carry separate color components is
now easily affordable; composite encoding is no longer
necessary in the studio. To avoid the NTSC and PAL
artifacts, to facilitate image manipulation, and to enable
compression, composite video has been superseded by
component video, where three color components R’G’B’,
or Y’C B C R (in digital systems), or Y’P B P R (in analog
systems), are kept separate. I hope you can manage to
avoid composite NTSC and PAL, and skip this chapter!
The terms NTSC and PAL properly denote color
encoding standards. Unfortunately, they are often used
incorrectly to denote scanning standards. PAL encoding
is used with both 576i scanning (with two different
subcarrier frequencies) and 480i scanning (with a third
subcarrier frequency); PAL alone is ambiguous.
In principle, NTSC or PAL color coding could be used
with any scanning standard. However, in practice, NTSC
and PAL are used only with 480i and 576i scanning,
and the parameters of NTSC and PAL encoding are optimized
for those scanning systems. This chapter introduces
composite encoding. Three later chapters detail
the principles: NTSC and PAL chroma modulation, on
page 335; NTSC and PAL frequency interleaving, on
page 349; and NTSC Y’IQ system, on page 365. Studio
standards are detailed in 480i NTSC composite video, on
page 511, and 576i PAL composite video, on page 529.
104 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES