How does Windows monitor calibration work? x-rite i1 Profiler

Started 1 month ago | Discussions thread
Simon Garrett Veteran Member • Posts: 6,593
Re: How does Windows monitor calibration work? x-rite i1 Profiler

Vunite wrote:

I got this x-rite calibrator thing and the newest software (i1 Profiler) for it. I reset the monitor to factory settings, I can run the calibration run, it does it's measurements and in the end seems to alter my monitors settings, as they're no longer the factory settings from before. And it lets me save a calibration profile to the windows system directories.

I'm assuming you're not using a monitor with internal Look Up Tables (LUTs) such as more up-range Dell, Benq, Eizo, NEC etc.  You can't use i1Profiler to calibrate those (unless it's a proprietary version from the monitor maker).

When you run i1Profiler (or any other software such as Argyll) two things happen:

  1. Calibration: the Tone Response Curve (TRC), and white point of the monitor are corrected to the desired TRC (e.g. gamma 2.2) and white point  (e.g. 6500K) by creating LUTs.  The LUTs are loaded into the video card at boot up. 
  2. Profiling: after calibration, the software measures the corrected TRC, white point and colour space of the monitor, and writes the result in a profile. 

With monitors with internal LUTs the correction LUT is loaded into the monitor itself, but this requires proprietary software.

After this, all programs will "look different", as the LUTs affect any program writing to the monitor.  However, only colour-managed programs will use the profile to get the correct colour.

Now I wonder about a few things:

1. If it alters my monitor directly,

It doesn't, unless the monitor has internal LUTs, and using proprietary software.

what do I need a windows software profile for? Does that change things in two places?

No.  The profile is simply a measurement of the characteristic of the monitor, and is required by colour managed software.

Colour managed software looks up the colour space of the image (from the image profile, e.g. sRGB, Adobe RGB...), and looks up the colour space of the monitor (from the Windows default profile, set by i1Profiler) and converts the image from one colour space to the other, so colours on the screen are correct

2. I have two different monitors. After saving the profiles in the x-rite software, I find both in the windows drivers system directories, but in the windows settings, both are assigned to just one monitor (?) and the other has no choices.

That's not right.  Windows allows a different default profile for each device.  When you go to control panel -> colour management there's a drop-down that allows you to select each monitor separately:

You can also see (but not set, I think) the profile in Settings -> Display if you have two monitors by clicking each monitor icon in turn.

3. There's x-rite software settings I'm not sure about, like having to chose light density.

I can't remember that setting (I can't check at the moment).  One setting you should alter: in "Profile Settings" change the profile version from v4 to v2.  Some colour-managed software won't work properly with v4 profiles.

A bit more info at http://simongarrett.uk/ColourManagementCheatSheet.htm

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Simon

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