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=cox.net@lists.apple.com> On Behalf Of Wire ~ via colorsync-users Sent: Friday, January 03, 2020 11:04 AM To: colorsync-users@lists.apple.com 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 < colorsync-users@lists.apple.com> 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=videotron.ca@lists.apple.com> On Behalf Of Wire ~ via colorsync-users Sent: January 3, 2020 12:12 PM To: colorsync-users@lists.apple.com Subject: Re: NEC PA271Q "Native" chromaticities

On Fri, Jan 3, 2020 at 7:54 AM <graxx@videotron.ca> 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 _______________________________________________ Do not post admin requests to the list. They will be ignored. colorsync-users mailing list (colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription:

https://lists.apple.com/mailman/options/colorsync-users/graxx%40videot ron.ca

This email sent to graxx@videotron.ca

_______________________________________________ Do not post admin requests to the list. They will be ignored. colorsync-users mailing list (colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription:

https://lists.apple.com/mailman/options/colorsync-users/wire%40lexipha nicism.com

This email sent to wire@lexiphanicism.com

_______________________________________________ Do not post admin requests to the list. They will be ignored. colorsync-users mailing list (colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/waynebretl%40cox.net This email sent to waynebretl@cox.net

Thank you guys for the clarifications! On Fri, Jan 3, 2020 at 1:18 PM Florian Höch via colorsync-users < colorsync-users@lists.apple.com> wrote:

Hi,

Am 03.01.2020 um 21:48 schrieb Wayne Bretl via colorsync-users:

...

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.

Note that "illuminant" here means the actual illuminant (not necessarily D50), not the PCS illuminant (which in ICCv2 and v4 is always D50). It's just another way of saying the color has not been adapted to D50.

Florian. _______________________________________________ Do not post admin requests to the list. They will be ignored. colorsync-users mailing list (colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription:

https://lists.apple.com/mailman/options/colorsync-users/wire%40lexiphanicism...

This email sent to wire@lexiphanicism.com

Am 03.01.2020 um 22:30 schrieb Wayne Bretl:> I guess it must have been necessary to invent the term for some reason,

probably related to use in LUT adjustment vs. color profiles (?).

But I really think saying "measured chromaticities" would be adequate (and not lead to a frantic search for a definition of the term "illuminant relative," which seems on its surface to imply some adjustment, when it really means the opposite).

Not wanting to invent yet another terminology, I copied that wording pretty much verbatim from the ICC spec, which is admittedly not necessarily meant for consumption by end-users. "Measured" would also be appropriate. Florian.