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Re: c/ Luma coefficients for DTV



On Jul 15,  8:13pm, Charles Poynton wrote:
> Subject: [TIG] c/ Luma coefficients for DTV
> Dear TIG -
>
> There is an issue that I think ought to be addressed in the transition to
> DTV and ATV: the choice of luma coefficients.
>
> The world has effectively standardized on a single set of RGB primaries
> (SMPTE 240M primaries and Rec. 709 primaries, surrounded by appropriate
> tolerance boxes). R'G'B' signals are effectively identical, independent of
> scan format, world-wide. (This even extends to computing.) SDTV and HDTV
> will code exactly the same R'G'B' values for a given image (or signal).
>



SMPTE240 and Rec.709 color primaries are different (even if you take
the tolerance of +/-0.005 in x and y into account) as well as the SMPTE240
and Rec.709 transfer functions are different.
.. In your book ("A technical Introduction to Digital Video") on page 148,
there is a matrix equation for RGB transform from SMPTE240(RP145) to Rec.709.

SMPTE 274M recommends, that the new equipment should be designed according
to Rec.709, but also includes the "interim implementation" paragraph which
allows to use the "smpte240 colors".


If R'G'B' are really "effectively" identical what is the actual
numerical error that can be tolerated here? (or what does the
"effectively" mean to different people?).


I design HDTV equipment that have to comply to known and accepted
standards .. and "effectively correct" is not good enough.

(I will appreciate any input on the subject)
Greg




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