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Apologies if this has already been asked, but I couldn’t find the answer I was looking for…
As far as I know, DisplayCAL Profile Loader uses the built-in Windows 10 Color Management to apply the .icm profile generated by DisplayCAL. So, what exactly does DisplayCAL Profile Loader do?
I see that it applies the profile numerous times while the application is loading. I’m assuming this is something the built-in Windows 10 Color Management doesn’t do by itself, right? But why exactly is this required?
Does DisplayCAL Profile Loader do something else that the Windows 10 Color Management doesn’t?
VCGT tag with grey calibration data is 16bit/entry. Some cards’ HW LUT cannot hold more that 8bit/entry, others can hold more.
Windows built-in LUT loader, i1profiler (and derivated products like Dell, viewsonic, etc), Basiccolor display and most of software that deals with loading data to video card LUT truncated data to 8bit/entry… which leads to banding.
Also once of these programs loads something to vidoe card LUT, it is truncated to 8bit unless you reboot.DisplayCAL (argyllcms) LUT loader can load calibration data to LUT at the highest precision available for that HW, so a video card with more that 8bit/entry LUTs and dithering at its output can show smooth gradients like a display with internal HW calibration.
Thank you. That’s one reason I can understand the motivation behind using DisplayCAL’s loader 🙂
Some follow up questions though…
- Why does it still use Windows 10 built-in Color Management?
- Why does it apply a profile so many times a day? I thought that that would only happen if the screen configuration changed but I’m 95% of the time with a single monitor in the same resolution. But it keeps applying the profile a lot when nothing changed in the screen.
1- What do you mean? DisplayCAL creates a profile, registers it as “default” profile for that display in OS. If it does not make that changes… you won’t be able to use PS/LR/etc properly. Color managed apps ask OS about display profiles. They need to know thatm GIMP and Firefox can be manually informed of that, but almots all others app do not. They ask OS, hence DisplayCAL needs to publish profile to OS color management system.
Maybe you meant “use built in LUT loader”, but DisplayCAL does not use it unless you manually choose that on profile instalation popup. And you are warned to DO NOT USE IT, and to use DIsplayCAL’s loader instead.
2-There are apps, full screen apps mostly, that reset video card LUTs. DisplayCAL reloads periodically LUTs to ensure calibration is not reset to no calibration. There is no OS notification queue for such changes, if one app resets LUTs, DisplayCAL cannot notice it. Hence it reloads it periodically.
If a buggy GPU driver causes issues in your particular computer because of these reloads you can disable it and force 1 load though DisplayCAL on each startup… but it is not user friendly.
Maybe you can ask for an DisplayCAL feature “load just one on startup, them I as user will check if calibration is reset”. Maybe such feature exist now, i did not check.Maybe you meant “use built in LUT loader”
Maybe, I’m confused.
After reading about this I’m not quite sure about the differences between the ICC/ICM profile and a LUT. I guess they are different things and the former is properly applied through the Windows 10 Color Management tool (where color managed apps like Lightroom, Firefox, whatever, go look for the profile and use it) and the latter is something else that I’m not quite sure if I’m using it or even if I need it at all. Which begs the question if I really need DisplayCAL Profile Loader.
but DisplayCAL does not use it unless you manually choose that on profile instalation popup
I did not chose that option, of that I’m sure.
ICM stores display behavior after calibration. This is what color managed apps use. They ask “how dowes thas display behave?” and get profile info. With that info thet can “change” RGB values sent to screen. This is what you configure in OS settings regarding color management: which profile is asociated by default with each display.
ICM can store 1D LUT grey calibration too, it is VCGT tag inside ICM display profile. This is what Displaycal reloads. This is what WIndows built in loader, i1Profiler loader, etc fail to use properly. Hence it is recomened to use DisplayCAL VCGT loader instead of Windows’.
It just for VCGT loading. Profile is registered in OS for apps to use them using OS color management services.apps -> ask OS for profiles, IT IS NEEDED that OS knows display profile
DisplayCAL loader -> loads calibration into GPU in the best way its HW and driver allows you.
They are 2 different things. One is “pubish display info”, the other one is “load calibration that makes display behave that way”.
Ok, I think I understand things a little bit better now, but just one last question to make things clear for me.
Say that my only goal with calibration/profile was to get Adobe Lightroom to display colors more accurately (since my monitor is Wide Gamut and colors look more vivid than what they really are). I use DisplayCAL to calibrate my monitor R/G/B controls and generate a color profile that I use to configure my OS settings for my single monitor. Lightroom will then ask the OS for color profiles and display colors more accurately.
If this was my only use case, would I still benefit from using DisplayCAL Profile Loader for the 1D LUT grey calibration?
If this was my only use case, would I still benefit from using DisplayCAL Profile Loader for the 1D LUT grey calibration?
Yes, it fixes grey (white, grey neutrality, gamma). A “Profile only” may work too for LR/C1… but may mess wioth Photoshop or other apps, so profile + GPU calibration.
Also you cannot use your current display profile made with DisplayCAL WITHOUT using DisplayCAL loader: display and profile won’t match unless you load 1D grey calibration first. You can load it with Windows loader, but you’ll get banding (you may get banding too if your HW is not “good” for that task evne if you use DisplayCAL).
