[opendtv] Re: New Chips Improve Color TV Dramatically
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 29 Jun 2004 12:59:39 +0100
I'll endorse all that Jeroen says, the colour science is correct. But I'll
add one more thing:-
The transfer function (gamma curve) is vastly more important in colour
rendering than is the choice of primaries. I've worked in this field on
problems such as this for about 25 years now, and I never cease to be amazed
at just how powerful the transfer curve is. Arguing about the primaries in
non-linear systems is a real waste of breath, gamma is fully in control.
----- Original Message -----
From: <jeroen.stessen@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, June 29, 2004 7:47 AM
Subject: [opendtv] Re: New Chips Improve Color TV Dramatically
>
>
>
>
> Hello,
>
> I wrote:
> >> 2 SMPTE RP145: R=(0.630,0.340) G=(0.310,0.595) B=(0.155,0.070)
> >> 3 EBU T.3213: R=(0.640,0.330) G=(0.290,0.600) B=(0.150,0.060)
> >> 4 ITU R.709: R=(0.640,0.330) G=(0.300,0.600) B=(0.150,0.060)
> >>
> >> Note that the primaries
> >> vary only insignificantly between these 3 standards!
>
> Mark Schubin wrote:
> > I do not dispute that there is only minor variation between the
> > primaries for 2-4, but I dispute that the chart allows us to come to
> > that conclusion. These coordinates are not on a perceptually linear
> space.
>
> Come on, Mark, the differences are small in ANY space.
> I was just trying to make a couple of points here:
> - there practically IS no difference between the primaries
> in the USA and those in Europe, and
> - there practically IS no difference between the primaries
> of SDTV and those of HDTV.
>
>
> There is however a large and unfortunate difference between
> the coefficients of the Luma Function between ITU-Rec.601
> (SDTV) and ITU-Rec.709 (HDTV):
> Y' = 0.299 * R' + 0.587 * G' + 0.114 * B'
> versus
> Y' = 0.2126 * R' + 0.7152 * G' + 0.0722 * B'
>
> The first formula was derived from the luminosity of NTSC
> primaries, the second one was derived from that of Rec.709
> primaries. However, since the derivation is only valid in the
> linear-light domain but the formula is applied in the gamma
> domain, it is largely irrelevant which values are chosen.
> Poynton argues that it was senseless to change the values,
> it only leads to confusion and errors.
>
> So if you ever see wrong colours and you suspect that it is
> due to the difference between two standards: blame the Luma
> Function, not the colour primaries. Because the primaries
> are really not that different.
>
>
> Of course, really different primaries CAN make a real
> difference. Only problem is: hardly anyone is using them yet.
> There are some efforts regarding conversion from a signal
> with standard primaries to a display with non-standard
> primaries, witness our own Philips-Genoa LCoS displays and
> various 4- and 6-primaries direct-view LCDs. There are some
> efforts about new standard primaries in relatively closed
> applications (digital cinema, digital photography, ... ?)
> but nothing seems to be happening in (digital) television.
>
> But note that it is not necessary to define new primaries !
> Any wide-gamut signal can be "compressed" into a standard
> colour gamut by attenuating the colour-difference signals
> (in the linear-light domain, of course) while converting
> (3x3 matrix) from the space of the wide-gamut primaries to
> the space of the standard primaries. This yields valid RGB
> signal values, to which the normal gamma correction can be
> applied. (No need for the extended function of e-sRGB.)
> Effectively this allows you to go outside the triangle.
> At the receiver side, the opposite transformation can be
> applied. Standard receivers (with a standard colour gamut)
> would display a slightly undersaturated picture. That is
> the simplest form of gamut mapping: linear de-saturation.
> Advanced receivers can apply a more accurate gamut mapping,
> and that is the only place where knowledge about the actual
> display primaries is needed. Not earlier.
>
> Let's write a new wide-gamut transmission standard ?
>
> Regards,
> -- Jeroen.
> |-----------------------------+---------------------------------------|
> | From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
> |-----------------------------+---------------------------------------|
> | Building: SFJ-5.22 Eindhoven| Philips Digital Systems Laboratories |
> |-----------------------------+---------------------------------------|
> | Phone: ++31.40.27.32739 | Visiting & mail address: Glaslaan 2 |
> |-----------------------------+---------------------------------------|
> | Fax: ++31.40.27.32572 | NL 5616 LW Eindhoven, the Netherlands |
> |-----------------------------+---------------------------------------|
> | Pager: ++31.6.6513.3818 | Visit us: http://www.pdsl.philips.com/|
> |-----------------------------+---------------------------------------|
>
>
>
>
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