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Old 10th July 2008, 16:48   #1  |  Link
pitch.fr
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Join Date: Jun 2008
Posts: 239
gamut conversions through Avisynth ?

hello world,

there's a new SAMSUNG projector, that's ISF(Imaging Science Foundation) certified and made under the supervision of Joe Kane(he's quite a video guru)

that's the SP-A800B(DLP 1080p), and as they say "Paramount, DreamWorks, ABC, and Universal Studios are among the professional users of this model."

http://www.projectorcentral.com/Samsung-SP-A800B.htm

it's one of the very few projectors(if not the only one) where you can change the gamut on the fly.

mostly, the SD movies are encoded through the REC601 matrix, and the HD movies through REC709.

but this is the theory...

in practice(and I know that sounds crazy), the mastering engineers still use this kind of monitoring displays :



the engineer is using a BVM CRT monitor(with SMPTE-C phosphores gamut)

this thing :

http://www.sony.co.uk/biz/view/ShowP...site=biz_en_GB

so basically, SD and HD movies are not mastered on sRGB/HDTV gamuts as we've all been led to believe.

video monitors used in Europe :
SONY BVM-A14F5M (EBU phosphores)
SONY BVM-A20F1M (EBU phosphores)
SONY BVM-A32E1WM (EBU phosphores)
SONY BVM-L230 (LCD)
SONY BVM-L420 (LCD)

and in USA:
SONY BVM-A20F1U(SMPTE-C phosphores)


so basically, to see movies the way they were mastered, you'd need :

1)YCbPr decoding :

- Rec. ITU-R BT.601-5 for SD primaries (in theory only)
Y’ = 0,299R’ + 0,587G’ + 0,114B’ (601)

- Rec. ITU-R BT.709-4 for HD primaries (in theory only)
Y’ = 0,2126R’ + 0,7152G’ + 0,0722B’ (709)

2)display gamut :

- REC-601 SMPTE-C for SMPTE-C primaries (NTSC SD & HD, 90% of bluray discs as well, and some PAL DVD's)

- REC-601 EBU Tech. 3213 for EBU primaries (PAL/SECAM SD and european bluray discs)

- REC-709 HDTV (for US and EUR HDTV)


that's what my DLP projector looks like, when calibrated in sRGB(the gamut is identical to the HDTV gamut) :



and here's a gamut comparison :



so is there any AVS guru that'd be interested to find a way to get 1:1 colors with the way movies are being mastered in the first place ?

of course it'd have to 10bit if possible in order to avoid banding and stuff.

I know that sounds crazy, but that's the way it is.
this Samsung projector is the ultimate thing to watch movies "the way they were meant to be watched"(it supports sRGB/HDTV/EBU/SMPTE/etc.. gamuts).

surely enough, you could revert this colorspace hiccup in AVS ?

....and run it in realtime in ffdshow ? that'd be the shiznit

here's a list made by the french ISF CEO "Julien Berry", that lists which gamut has to be used for each Bluray movie :

http://www.wysios.com/jkp/gamut2.asp

from what he told me, here's what happens when using a display with sRGB/HDTV gamut :

Quote:
for telecines that were made on an EBU monitor, only the green primary will be off.

for telecines that were made on an SMPTE-C monitor, the colors will be over-saturated.
when you read that most of the bluray's are made on SMPTE-C monitors, and that usually you end up with over-saturated colors on sRGB/HDTV displays.....that suddenly would make a lot of sense to fix the colors.....wouldn't it ?

here's a technical PDF about gamuts :
http://www.teksite.co.kr/osilo/down/...nd%20gamut.pdf


and basically you can do this gamut conversion with a scaler :
http://www.google.com/search?hl=en&q...tnG=Search&lr=

its job is to convert gamuts, but that costs a hell lot of money(and usually only SDI input and DVI output).....so doing it in AVS in 10bit would be beyond words

some ppl have worked on it with PS scripts :
http://www.avsforum.com/avs-vb/showthread.php?t=912720

the idea would be to :

-do REC-601/REC-709 matrix conversions for SD/HD to get sRGB content
-do REC-601 SMPTE-C / REC-601 EBU Tech. 3213 > HDTV gamut conversions to get proper primaries on sRGB/HDTV displays

Last edited by pitch.fr; 13th July 2008 at 23:50.
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