DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

It’s sensible to use the term
colorbar test signal (or pattern)
instead of colorbar test image:
The image is not standardized.
System
Primary
chromaticity
Transfer
function
Luma
coefficients
480i SMPTE RP 145 Rec. 709 Rec. 601
576i EBU Tech. 3213 Rec. 709 Rec. 601
1035i
720p,
SMPTE RP 145 SMPTE 240M SMPTE 240M
1080i,
1080p
Rec. 709 Rec. 709 Rec. 709
Table 24.1 Chromaticity, transfer function, and luma
combinations circa 2002 are summarized.
In my view, it is extremely unfortunate that different
coding has been adopted: Image coding and decoding
now depend on whether the picture is small (conventional
video, SDTV) or large (HDTV); that dependence
erodes the highly useful concept of resolution-independent
production in the Y’C B C R 4:2:2 and 4:2:0 domains.
In my opinion, Y’C BC R should have been standardized
with C B and C R having identical excursion to luma, and
HDTV should have been standardized with the Rec. 601
luma coefficients. With things as they stand, the smorgasbord
of color-encoding parameters makes accurate
image interchange extremely difficult. The situation is
likely to get worse with time, not better.
Table 24.1 above summarizes the standards for primary
chromaticities, transfer functions, and luma coefficients
that are either implicit or explicit in several SDTV and
HDTV standards. When video is converted among these
standards, appropriate processing should be performed
in order to preserve the intended color.
It is a problem that the colorbar test signal is standardized
in the R’G’B’ domain, without any reference to
primaries, transfer function, or luma coefficients. The
colors of the bars depend upon which primary chromaticities
are in use; the luma and color difference levels
of the bars depend upon which luma coefficients are in
use. When color conversions and standards conversions
are properly performed, the colors and levels of
the colorbar test signal will change!
CHAPTER 24 LUMA AND COLOR DIFFERENCES 297