RE: NEC PA271Q "Native" chromaticities
RE: NEC PA271Q "Native" chromaticities
- Subject: RE: NEC PA271Q "Native" chromaticities
- From: Wayne Bretl via colorsync-users <email@hidden>
- Date: Fri, 3 Jan 2020 13:48:55 -0700
From what I read here:
https://sourceforge.net/p/dispcalgui/discussion/932494/thread/67db9b70/
"illuminant relative" refers to direct measurements of the display
chromaticities without an adaptation adjustment, although that name then
doesn't make sense to me.
A CIE graph of measured chromaticity does not need to be referenced to an
illuminant, but the same chart may be used to plot apparent chromaticities as
adjusted by a Bradford adaptation.
You wrote: " Continuing my BS guess is that the only way to backtrack from xy
coordinates to some spectral power distribution is under the assumption of an
illuminant?"
No, there is NO WAY to backtrack from xy coordinates to a spectrum. This is the
basic premise of color reproduction, that many different spectra may have the
same xy coordinates, thus, the display does not need to match the original
spectrum, but only produce the same cone cell stimuli as the original, using a
mixture of three display primary (RGB) spectra.
-----Original Message-----
From: colorsync-users
<colorsync-users-bounces+waynebretl=email@hidden> On Behalf Of Wire
~ via colorsync-users
Sent: Friday, January 03, 2020 11:04 AM
To: email@hidden
Subject: Re: NEC PA271Q "Native" chromaticities
Re calling out illuminant:
I'm not up to speed on why DIsplayCal calls out "illuminant relative", so I
included in case it affects the interpretation.
The numbers I supplied are stored in the profile made by DisplayCal and
accessed using the companion app ICC Profile Info.
I'm not clear about the science, but my thought is that because the whole
diagram is a model of perception, and there is visual adaptation, then a CIE
graph always has to be referred to some illuminant, e.g., the standard
illuminant? Honestly I am just BSing here, and would like to understand this
more. Continuing my BS guess is that the only way to backtrack from xy
coordinates to some spectral power distribution is under the assumption of an
illuminant? Given that display white point is variable, then maybe this is just
being super clear that it's referred to the target of the profile. I should
should shut up...
Re uniformity:
The unit certificate (Dell's cal report that comes in the box) claims Dell
measured < 2 dE across board, with a report focus on uniformity, saying the
report is based on a feature called "Display Uniformity Compensation" being
enabled. However some modes—at least Custom Color (native)—disable this feature.
My report of a whitepint variance across the panel left/right (which while
unwanted seems typical of the IPS tech) was using the display in native mode,
so uniformity compensation was off. I assume the Adobe RGB mode enables it, but
I didn't think to check white uniformity when I ran the Adobe RGB cal. I don't
know how it works.
Re your previous messages with NEC / NTSC XY plots. I chose the UV plot for
better perceptual accommodation when comparing 2D gamut coverage. The slight
Green deviation you noted in a previous message will be more accentuated by an
XY plot, but this also inflates its significance in the plot as compared to the
other primaries. I understand what you were looking
for: the engineers had to make a tradeoff to get the panel to do both Adobe and
P3, so there's a tiny bit of missing coverage in one vs the other.
Irrelevant to user, I think.
Basically—if my measurements and report can be trusted—this display appears to
cover the popular use cases when combined with custom profiles in native mode.
It has a great stand, including rotation. And does HDMI/HML and DisplayPort
with DDC/CI. And it has a high current USB3 hub!
Looking at the user guide, Dell sells a branded i1d2 and "PrecisionColor"
app that appears to know to interact with the display via DDC/CI so that SW can
select personalities. What would be cool is if you could load a custom profile
into the internal LUT. But I don't think it supports this.
In a nutshell, it does what's claimed, it looks gorgeous to me. And at $300
delivered, it seems a good buy. Very pleased.
On Fri, Jan 3, 2020 at 9:21 AM Roger Breton via colorsync-users <
email@hidden> wrote:
> I take it that 'Illuminant-relative' means the actual (raw) values
> returned by the instrument?
>
It's almost on the nose of the NEC PA271W chromaticities, practically the
> same 'gamut'.
> For a whole let less money. But what about the 'uniformity'? Can't say
> how comparable it is, for I don't have a PA271W but that's an
> important quality.
> / Roger
>
> -----Original Message-----
> From: colorsync-users
> <colorsync-users-bounces+graxx=email@hidden> On Behalf
> Of Wire ~ via colorsync-users
> Sent: January 3, 2020 12:12 PM
> To: email@hidden
> Subject: Re: NEC PA271Q "Native" chromaticities
>
> On Fri, Jan 3, 2020 at 7:54 AM <email@hidden> wrote:
>
> > Are you able to post the measured RGB chromaticities?
> > / Roger
>
> Dell UP2516D primaries as measured using DisplayCal / Monaco Optix
> DTP94
>
> I haven't sanity-checked these numbers, so if something looks weird
> please say so...
>
> Display in native mode:
> Chromaticity (illuminant-relative)
> Channel 1 (R) xy 0.6829 0.3123
> Channel 2 (G) xy 0.2256 0.7248
> Channel 3 (B) xy 0.1515 0.0486
>
> Display in Adobe RGB preset mode:
> Channel 1 (R) xy 0.6441 0.3301
> Channel 2 (G) xy 0.2278 0.7157
> Channel 3 (B) xy 0.1515 0.0562
>
> /wire
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