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Old 17th August 2019, 04:03   #89  |  Link
hello_hello
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Join Date: Mar 2011
Posts: 4,823
poisondeathray,
Thanks for the reply.
Maybe I'm being thick, but I'm still not 100% clear on this.

Even the section you quoted only refers to HD and SD colorimetry, implying SD is a single colorimetry.
The pdf appears to me to explain the method for converting analogue to digital. Below figure 2.6 it says:

Chromaticity coordinates specified are those currently used by 625-line and 525-line conventional
systems.


I doubt any of us are using 625 or 525 line displays any more, and it seems the colorimetry co-ordinates convert "from" those systems. Even if they're different in analogue form, it seems bizarre to use two formulas to convert them to different digital SD colorimetries rather than them ending up the same. If they're not intended to convert to the same colorimetry, why use different formulas?

I must be missing the obvious here, and I won't get a chance till tomorrow, but I'll do some more reading to see if I can work out what I'm missing. In the mean time though, if there's two rec.601 colorimetries in digital form, which one do programs with only a single rec.601 option normally use?

Cheers.

PS. I've had the table in the ColorMatrix help file in my head, which is one reason I'm confused about it now. To me it implies there's only a single rec.601 in digital form but maybe I've been mis-interpreting it.

Quote:
This is a list of all possibilities according to the MPEG-2 specs and DGDecode.
0 forbidden
1 ITU-R BT.709
2 Unspecified Video (unknown)
3 reserved
4 FCC
5 ITU-R BT.470-2 (exactly the same as ITU-R BT.601)
6 SMPTE 170M (exactly the same as ITU-R BT.601)
7 SMPTE 240M
8-255 reserved

Last edited by hello_hello; 17th August 2019 at 04:11.
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