ColorHug2 / DisplayCal / Dell Ultrasharp UP2716d

[Ari]

New colorhug 2 user, trying to calibrate/profile my up2716d monitor. This panel has GB-LED backlight.

I'm learning to use argyll displaycal on Fedora 24. I set it to Gamma 2.2, D6500.

Displaycal detects colorhug2 and offers a list of "modes". Modes include LCD (Generic), LCD (Whilte LED), Factory Calibration, and a few others

Questions...

 - which colorhug2 mode should I use?

 - do I need a ccmx file? Tried to find one in argyll's database but no luck

 - I notice that in displaycal, without setting a target temperature (uses the native one I suppose, 10K as included in the icc profile) the AdobeRGB coverage is 96%; when setting the temperature to D6500, it doesn't go past 91%, is this normal?

- Colorhug Display Analysis results for coverage are quite different the info contained in DisplayCal icc metadata - e.g. displayCal tells 91% of AdobeRGB, and colorhug tells 85%, which is more accurate?

- Sorry if this is a basic question: after calibrating to D6500, I got the impression that the display is a bit reddish; seeing that I'm going from 10K (factory) to 6.5K (calibrated) I'm assuming that this is a normal perception and not the "colorhug v1 red tint problem", but how can I confirm this?


Thanks

[Ari]

Answer to self: I was indeed seeing the dreaded red-shift. This was evident in DisplayCal gamut visualization (and on any icc gamut viewer), where the gamut "triangle" of the display (vs. sRGB and aRGB) was entirely red-shifted leaving blues and greens out of the supported gamut.

By pure chance I set DisplayCal to go fully Automatic for a test run, and noted that this created a CCMX file based on the this monitor EDID. Looks like the EDID info was accurate because since then the red-shift is gone, with DisplayCal reporting > 99.9% AdobeRGB coverage which is what the manufacturer advertised. This is valid also for D6500 calibration. Calibration results are reproducible; I ended up with two ICC profiles, one for daywork (brightness 75%) and one for evening work (brightness 50%) and really happy with the results, both covering 99.9% of aRGB. I checked Gamma and color reproduction with various online tools and all are looking fine. Also the resulting calibration is a refinement of the factory (aRGB) calibration (this display comes pre-calibrated from the factory with DeltaE < 2)  instead of a complete change toward Reds as was happenig before using the CCMX file.

In DisplayCal, I'm now using:

• Instrument = ColorHug2
• Mode = Factory Calibration
• Correction = Auto (which picks up the ccmx file: Matrix: ColorHug2 & Dell (EDID) AUTO)

My use-case for accurate color reproduction is mainly Darktable - I'm happy now with ColorHug2 and this display. Color-wise the display is just nice; as reported elsewhere, brightness "uniformity" (as measured with DisplayCal) is so and so (+-12% brighness variance accross the screen) but that wasn't a surprise.

The only thing that I couldn't really get to work is the "ColorHug Display Analysis" (CHDA) tool: after calibrating the display using the CCMX file, the results of CHDA went completly off: it detects 0% aRGB / sRGB coverage and a totally wrong white point temperature (9300K vs 6500K). I tried uploading the CCMX to ColorHug2 with the command line tool,

colorhug-cmd set-calibration-ccmx 1 "ColorHug2 & DELL UP2716D (EDID) AUTO.ccmx"

And then selecting it with both the GUI (CCMX loader) and via command line:

colorhug-cmd set-calibration-map 1 1 1 1 1 1

But this produced no change in the CHDA  results. Interestingly, with my initial DisplayCal calibration/profiling (the one that used no CCMX) and required significant R/G/B gain correction to set the whitepoint, the CHDA whitepoint and coverage readings coincided with DisplayCal's. It could make things easier if CHDA could just accept a CCMX file on-the-fly as DisplayCal does.

I attach the ccmx file I'm using in case anybody finds it useful, as I have found no previous references of UP2716d calibration/profiling with ColorHug.

[ma...@nipltd.com]

Useful as a work around - I've had to resort to "Automatic" too. Very frustrating to have to resort to it and that my ColorHug2 can't be used for whitepoint setting with the LCD monitors I've tried it on though!

I ordered a ColorHug2 towards the end of last month. I've now tried it with 4 different LCD monitors (none are wide gamut) going for D6500 and on each I get the red-shift. With all four screens when I use DisplayCal and mode LCD (generic) or mode LCD (white LED) as appropriate then on the interactive display adjustment and the green bar is very high compared to the red and blue (which are usually about the same).

The monitor models are as follows (some are quite old, the IPS one is brand new):

LG 24MP88HV-S (that's the IPS panel with white LED backlight - claims 99% sRGB and is factory calibrated with a report included in the box)
LG W2361V
Acer x193W
Dell Ultrasharp 20inch 2007FP

A couple of those monitors were calibrated on different computers - all mostly tested using DisplayCal and gnome's colour calibration from Ubuntu Xenial, but also a couple of them tested using the USB live distribution that came with the ColorHug2.

With one of the monitors I took photos of it displaying a white patch both before and after calibration (so pre calibration and post calibration resulting in red shift) using my DSLR set to a white balance of 6250K (the camera doesn't have a 6500k setting) and with a piece of white A4 paper lit by daylight in the same shot. Not very scientific or accurate, but the results seemed to confirm that the monitor had a default white point was in the ballpark of 6500k and that the colourhug2 was giving results with too much red in (couldn't really be sure about the relative levels of blue and green).

Similar to your results with aRGB coverage, but with sRGB instead on my "99% sRGB" monitor - with the calibration that resulted in a reddish tint then  the results from DisplayCal were somewhat less than 99% of sRGB, but if I used "Auto" with the monitor's default colour balance so DisplayCal generated its own CCMX then the coverage was reported was at least 99% sRGB.