Profile a display without calibrating first

Software darktable
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I use Darktable so I think this is the correct place to post this, please feel free to move it if there is a more suitable place.

Question 1. After profiling with displaycal, an information box shows the sRGB gamut and the sRGB coverage. What is the difference between gamut and coverage?

Question 2. After much reading of the Argyllcms docs, Displaycal docs, ninedegreesbelow web site and experimenting with calibration & profiling, I think I might be getting a better profile if I do it like this;

Leave the monitor at default settings, so R, G & B are left at 100%.
Lower the monitor brightness to something comfortable (140cdm ish for me).
In displaycal, set white point, gamma and luminance to ā€˜as measuredā€™.
In displaycal, make the profile.

On completion, it reports and sRGB coverage of 105%.

Previously, when I set displaycal white point to D65, luminance to 120cdm, gamma to 2.2, followed by adjusting the monitor R, G , B & brightness while calibrating, I end up with a profile that has sRGB coverage of about 90%.

My display native white point is about 5600k, as shown if I run a report on uncalibrated display. Itā€™s noticeably bluer than when I calibrate to D65, but in all honesty after about 10 minutes my brain has adjusted. When I switch back D65 it is noticeably yellower, but again I soon adjust.

Regardless of how I calibrate, provided I donā€™t go stupid, both profiles are perfectly useable within darktable.

So the question is, what calibration settings are you using before profiling?

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Hmm. D65 is bluer than 5600K. How come you see the opposite? My understanding of colour management is rather limited, so maybe the problem is with me.

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How was your accuracy?? You might achieve greater coverage or gamut with one approach vs another but it might be at the expense of color accuracy. also I thought most monitors today were closer to d65 natively than what you found?? Interestingā€¦

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If using 5600 as measured as the wp then more blue will be added to correct colors in the profile one might think but like you not really sure but maybe that is what he is seeing??

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Does your monitor actually cover 105% of sRGB?

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The way I understand it: when one uses DisplayCal, and first calibrates the display, then one uses the displayā€™s controls (e.g. RGB settings) to bring the display closer to the calibration target (for example, in this case, D65). For a display with a native white point at around 5600 K, that would mean reducing red to make the display bluer. However, if you skip that, and profile your display with 'as measuredā€™, it means your white point will remain at 5600 K; the white point of sRGBā€™s 6500 K will be shown as 5600 K, instead. The other colours (sRGB RGB coordinates) will be converted to XYZ, then transformed using the same D65 ā†’ 5600 K shift, and the resulting XYZ coordinates will be transformed to the display RGB values. But that may be totally wrong, so Iā€™d be grateful if someone, who actually knows this stuff, corrected or confirmed it. :stuck_out_tongue:

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As I understand it you are correct. I think if you donā€™t correct the wp during that intial part ie the calibration then the profiling part ie the mapping of the colors will be impacted by that. I think an easy visual check other than the reports will be the grey rampā€¦a color cast on the white , greys and or black would to me indicate not the best profile and that might not show up as clearly in the color but should show up in the grayā€¦

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I use the Adobe RGB values, but with the white point luminance reduced to 100 nits:

White point: D65
White point luminance: 100 nits
Black point luminance: 0.35 nits (contrast ratio ~300:1)

Repeat adjustment of monitor settings as needed to satisfy all three conditions.

Then profile to gamma 2.2.

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I also use D65, gamma 2.2, and as measured luminance (a level thatā€™s comfortable to me, fairly dark, as I usually edit in the evening / at night).

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For my information, could you post a screen-shot of the information box, please?

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@kofa Hmmm, now you have got me wondering, I need to double check.

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What software do you use when you do these sorts of comparisonsā€¦you have done a few I thinkā€¦just curiousā€¦

I see that these quite famous tools are now Freeware as of the new yearā€¦ I know not opensourcedā€¦but some might be interested

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I bought the cheap version of ā€˜ColorThinkā€™ (not PRO), long ago:

Thanks for the BabelColor ref!

1 Like
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Thanks all for jumping in. The Argyllcms docs are a heavy read. I read that better results ā€œmightā€ be obtained by using the displays native gamma and white point. MIGHT being the operative word. I decided to experiment.

@priort Where is the acuracy reported? I will check it. I am using displaycal to profile, colord to manage display profile and darktable darkroom to compare results.

@cedric I will upload screenshots, no prob.

@paperdigits I have no idea if it actually covers 105% of sRGB. I am just getting to grips with this, itā€™s early days. How do I check?

I think I will start again one evening during the week. I will set everything back to default, delete my experimental profiles, go step by step and post screenshots, then ask for feedback from you guys if thatā€™s OK? I broadly understand the concepts but am clearly having trouble interpreting the results.

1 Like
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Which calibration device do you use? Spyders before the X are terrible and canā€™t be relied on to give an accurate reading.

Which monitor?

I followed the recommendations in this tutorial: https://phototacopodcast.com/photographers-guide-to-screen-calibration-with-displaycal/

The manufacturer should have the specifications, but you should also be able to find them here: https://www.displayspecifications.com/

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@Donatzsky Monitor is an Acer K272HL, just a basic monitor. Colorimeter is a Colormunki Display.

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Bruce Lindbloom knows everything about color:

http://www.brucelindbloom.com/index.html?ColorCalculator.html

I set sRGB to 1,1,1 e.g. as white as it gets. Then D50 then D65. in CIE xyY space it shows:

D50: x,y = 0.345669, 0.358496
D65: x,y = 0.312727, 0.329023

In terms of color temperature, the above shows the D50 is ā€œwarmerā€ than D65 and, in any case, his Calculator shows 5000K and 6500K when changing the illuminant.

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Out of interest, I downloaded the patch one and the other one. Both failed to open on my machine (dell 4-core, Win 7) - missing .dlls, so I trashed them. No, Iā€™m not upgrading my Win version yet.

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You likely need 32bit then or yep your os is too old

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I couldnā€™t find any information on sRGB coverage anywhere, which probably means itā€™s not great. But VA panels are in principle capable of larger-than-sRGB gamut coverage, so who knows.