Struggling to Understand Color Management

Hardware
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I just bought a fancy new monitor with a built-in hardware calibrator. My naive thinking was, if the monitor calibrates itself, I’ll just need to set the OS to use a generic color space, and won’t need to software-calibrate the OS any longer. But the desktop calibrator and the screen calibrator seem to disagree. After half a day of head-scratching I come to you for help.

For a long time, I’ve used two BenQ PD2700U screens, calibrated using dispcal with my very old ColorMunki Smile. The two screens don’t match perfectly, but it’s close enough. Now I wanted to treat myself to a nicer screen, and bought an Asus ProArt PA27UCGE, which comes with a built-in hardware calibrator.

Since the screen is thus supposed to be well-calibrated, I set the screen to sRGB mode, and just selected the built-in sRGB profile in macOS.

But, the colors do not match.

The Asus is decidedly more green than the BenQ. Running through the calibration routine with dispcal and the colorimeter indeed lowers green a lot, at which point the colors on the BenQ and the Asus match.

But… who is right? How to tell?

So I compared against other probably-good screens, such as my wife’s MacBook screen, and my Surface tablet screen. The desktop-calibrated white point matches that of the MacBook, whereas the Surface white point is somewhere else yet. My “professional” 8-ink Canon Pro200 printer seems to lean more towards the Asus white point.

I wouldn’t trust that ColorMunki Smile colorimeter all that far. It is pretty old, and was cheap. All things considered, I’d have thought that the €800 Asus screen should have a better built-in colorimeter than that. But the ColorMunki seems to agree with the MacBook display. But I just can’t imagine the Asus screen being so entirely off, either! And it does seem to agree with the printer.

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For now, I’m just trying to set everything to sRGB, as neither Darktable nor Digikam can read the display’s native profile.

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This is almost certainly wrong, your calibration should have given you a profile, you need to use that profile.

Also I would suspect that there is some mode for the screen that uses something better than just sRGB, but I am not 100% on that.

The part that took me a while to understand is that you should never set your computer system’s profile to some generic profile, like sRGB, as that is telling you system that “my monitor is pefectly sRGB” which will never be true (most likely). The ICC profile generated during calibration is the difference in color and contrast between what the monitor shows and the known colors being measured. The ICC profile generated and then used by your system corrects the monitor back towards the known colors used to profile.

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Actually, I think the display profile for the monitor says, ‘this is the gamut for this display’, and the software then uses that profile as the destination for the display transform.

Since the screen is thus supposed to be well-calibrated, I set the screen to sRGB mode, and just selected the built-in sRGB profile in macOS.

This is most certainly not using that monitor to its full color potential, at the very least.

At its essence, color management is about scrunching the large camera spectral response down to a gamut corresponding to what the rendition medium (in this case, your display) can handle. So, the last profile in that chain should be one that corresponds to the display’s color capabilities.

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I was actually hoping that that was exactly the point of the hardware calibration and hardware LUT. But you’re probably right, it doesn’t work like that.

Yes, that’s most certainly true. The monitor can do close to the full DP3 gamut. But before I delve too deeply into that, I want to at least get the basics right.

Also, most of my output does go to the web, so I’ll probably continue to limit myself to sRGB most of the time.

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Or you could assume that all recipient equipment is properly color-managed and post images with whatever profile suits you.

Elsewhere it is noticeable that some people post their images with Adobe RGB (1999) but my browser takes care of that.

This one was posted here with the ProPhoto profile, how does it look?

SDIM0431
SDIM04311168×784 1.13 MB

No need to tell me that not everybody has perfect color-management …

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That’s more recently the case now, as the browsers have seem to settled on converting to sRGB by default. Yep, the best thing anyone can do is to embed the profile corresponding to the image encoding in the file, so other folk at least have the information needed to color-manage.

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Check out the art is right YT channel…he does lots of videos on calibration and Asus primary monitors…

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Can you explain why that is a problem with a hardware LUT based monitor?

If I understand correctly the chip inside the monitor does all the remapping from the input to the display color “profile”. So if the OS just pipes perfect sRGB, but your display is not perfect, the chip does all the remaps instead of the OS (via icc profile).

I am obviously missing a step, but I dont know where to start trying to figure out what I am missing.

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I assumed that @bastibe used displaycal, which is not a hardware lut solution as far as I know. Some clarity there would be helpful.

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I’ve made some progress this morning. There is indeed documentation on ASUS’ part, which states that you’re supposed to choose the desired profile in the monitor (say, Display P3 or sRGB), and then select the appropriate generic Display P3 or sRGB profile in macOS. Asus says to download the generic profiles from their website, by they seem to be missing.

Last night, I finally found those generic profiles. They do not show up in the list of available downloads:

Screenshot 2025-07-20 at 09.16.28
Screenshot 2025-07-20 at 09.16.282532×1242 190 KB

Turns out, they are hidden behind the “Show all” link :man_facepalming:.

So, that part at least is sorted. Now I can follow the documentation: Since the monitor has an internal, calibrated LUT, I don’t need to calibrate the OS side. All I do is to tell the OS about the color space, but there’s no additional LUT necessary in software.

I can now select either sRGB or Display P3 (or various others), and all my sRGB pictures show up correctly.

For now, Darktable on macOS limited to using sRGB due to a bug in Cairo and GTK. But it is properly color-managed in sRGB, so it renders identically for the monitor set up with sRGB and Display P3. So that’s good. That’s progress.

However, there is still the initial point of concern:

If I calibrate with discal (either screen), it comes out more magenta than the new screen. The 6500K white point in dispcal is different from the white point on the new screen (also set up to 6500K). The new screen seems to match my Canon printer, while the dispcal white point seems to match my wife’s MacBook screen.

To be clear, I am not using dispcal to calibrate the new screen, since it has an internal hardware LUT and does not need software calibration. I’m just using it to cross-check my results, and compare it to my second screen.

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Still trying to get to the truth of which white point is correct.

I thought I’d use my camera as a calibration device of sorts: I displayed a white surface on both screens, and calibrated my camera’s white balance to this surface. Then I took a picture with these two white balance settings, and checked how various photo editing programs report this “as shot” white balance:

Old Screen New Screen
Darktable 5712K 6144K
RawTherapee 5718K 6153K
DxO Photo Lab 5904K 6325K
Capture One 5466K 5809K
Affinity Photo 5719K 6132K

None of them are exactly 6500K, but the new screen certainly is closer to it. I’m not sure how useful this information is.

Also, I’m not exactly sure why Capture One is running at all. Its license is supposed to have expired long ago, but somehow it appears to not have noticed? Do I now own a perpetual free license to Capture One somehow?

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You got it w/ WinRAR license :crazy_face:

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Could it be that the ColorMunki Smile is one of those old devices with fading color filters? X-Rite has been using stable, inorganic filters for a long time now, but I know they did use organic dyes or something in a few devices.

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That was my first thought, I heard about Spyder filters fading too (I’m kinda lost in the rebrands, might be the same thing). Calibrite Display SL that I have should be of those stable ones, @bastibe you might want to look around if you can borrow one to confirm

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That’s what I’m leaning towards, too. The ColorMunki doesn’t have the best reputation, and it is quite old now. It would actually explain a few things… that I’ve probably biased my edits green for the last few years because of a faded colorimeter.

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Have you tried the color management in ART on mac using the built bundles? They are supposed to include a patched gtk from what I understand Release 1.25.6 · artpixls/ART · GitHub

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This may be useful (the stable filters of Display SL / i1DisplayPro are mentioned in the second link)

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Have you calibrated the screen using the vendor software (it updates the internal profile)? As far as I can tell, you are supposed to do this every-so-often. Its a new display so probably has not drifted but… shrug.

Do you need to produce color accurate digital deliverables for your work? For me the impetus for purchasing a better monitor was the benefits to my printed “workflow”. If the Asus matches up to the prints more closely, I would go with that. Your needs and use cases may be different than mine.

Color accuracy is, at the end of the day, something of a misnomer and really only important within the contexts you chose to prioritize. You could have a “perfect” set up, but that means nothing if nobody else does.

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This screen calibrates right within the monitor firmware, no desktop software needed. You can trigger it from the desktop as well, but it’s strictly optional.

None whatsoever. This is my hobby and nothing else. I do like a pretty print, though, and enjoy exploring these topics.

That said, I mostly work from home, and use this monitor every day for work. I will enjoy its rich contrast, high frame-rate, and great sharpness every day. In fact, I specifically chose this model as it’s not just color-accurate, but also high frame rate, which is very nice for gaming, and scrolling text. (This makes it tax-deductible, too, which is nice)