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Old 17th August 2019, 03:24   #88  |  Link
poisondeathray
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Join Date: Sep 2007
Posts: 5,345
Quote:
Originally Posted by hello_hello View Post

I read your reply in the other thread and looked at the PDF, and I can see rec.601_525 line and rec.601_625 line are different, but the question I'm trying to get a simple answer to is... why do other programs such as ColorMatrix & DitherTools only have/require one version of rec.601?
I assume my understanding is wrong, but I thought once analogue PAL and NTSC are converted to digital, the colorimetry is the same, and therefore there's only one flavour of rec.601 required for colorimetry conversions. When I play an NTSC DVD encode, is the same colorimetry being used by MPC-HC to convert to RGB on playback as for a PAL DVD encode?

StvG said in the other thread I should be using rec.601_625 to convert between HD and SD etc in digital-land, and I don't doubt him, but once again I'm just after a simple explanation as to why.

Cheers.

Simple answer is convention. It's the way everyone does it


1) Matrix for bt470bg (pal, or 601-6_625), smpte170m (ntsc, or 601-6_525) are the same, 709 different
2) Transfer for bt470bg, smpte170m, and 709 are the same
3) Primaries are different for all 3, but look at footnote 2

Code:
It is recognized that a practice is now sometimes used by which, when programs produced in HDTV are
release in SDTV, their HDTV pixel map is re-mapped onto the SDTV pixel map without changing the
colorimetry of the original program.
In practice, only matrix is usually accounted for, not primaries. You see this in professional HD to SD conversions, broadcast NLE's too . Technically you should adjust for the primaries too, but it's rarely done.

ie. So technically it's a HD => SD conversion with uncorrected 709 primaries .

But you can do whatever you want - you control matrix, transfer, or primaries for source/destination with tools like zimg/zlib (resize in vapoursynth, avsresize in avisynth)

dither tools' "newer brother" fron the same author, the vapoursynth's fmtc also give you control over these
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