X Rite i1 Display Pro

Started 4 months ago | Discussions thread
Simon Garrett Veteran Member • Posts: 7,164
Re: This is a very good question....

Ken60 wrote:

Thanks

Simon , so is it Adobe communicating directly with the LUT in the screen ..... or is it windows 10 ?

Well, neither really.

A monitor with internal LUTs can emulate another colour space, provided the emulated colour space is within the native colour space.  For example, a wide gamut monitor with a colour space of roughly Adobe RGB can emulate sRGB (which is entirely within Adobe RGB), but a monitor with a colour space of roughly sRGB can't emulate Adobe RGB, as that needs colours outside sRGB which the monitor can't display.

It does the emulation by mapping the RGB values sent to the monitor to the appropriate ones for its native gamut.  Suppose the LUT is calibrated so that the monitor with native colour space of about Adobe RGB  is emulating sRGB.  After calibrating the LUT to this sRGB emulation, then profiling will create a monitor profile of sRGB.

Suppose then a program displays fully saturated green.  A fully saturated green in sRGB has R,G,B values of 0,255,0.  But in Adobe RGB, the same colour will be something like 140,230,60.  The LUT will have entries to make that translation.

But: neither Adobe software nor Windows know anything about this.  They both just think they have an sRGB monitor. Well, Windows doesn't give a damn, but colour managed software will look at the monitor profile, which will be sRGB or similar, because that's how the monitor is calibrated in this example.

after all you have to have a win icc to tell it to leave stuff alone and send all channels full tilt.

That's not what happens.  A profile is a description of the colour space of a device.  It tells colour managed programs the colour space of the device - monitor, printer or whatever.

Again it is said that to go from one profile to another you need to adjust the win icc, interesting because it is just a blank anyway, all the head work is in the monitor's lut ?

Not quite.  A profile is a measurement of the colour space of a device (also contains information about white point, Tone Response Curve (TRC) and a few other things).  That information is never blank.

For a monitor that doesn't have internal LUTs, then the graphics card can provide limited calibration of white point and TRC.  Graphic cards have 1D LUTs, which can't map colour spaces (that needs 3D LUTs) but can map white point and TRC.  In that case, calibration generates LUT information for the graphics card (as opposed to the internal LUTs of a monitor that has them).  That calibration LUT information doesn't strictly "belong" in a profile, but years ago Adobe invented a "vcgt" entry (video card gamma table) in icc profiles that is used to store the LUT info.  That vcgt info is read and loaded into the graphics card LUT at boot up.

For a monitor that does have internal LUTs, the video card doesn't need anything loaded into its LUTs, and the vcgt calibration in the profile is blank, but the colour space information is still needed.

To go from one profile to another: if you have a monitor with internal LUTs, in other words a monitor that can emulate different colour spaces, then if you change from one emulation to another, you have to do three things:

  1. Change the LUT calibration.  On most monitors with internal LUTs you can store multiple calibrations and switch between them with a front panel button, or sometimes by a utility program.
  2. Change the monitor profile in Windows to the appropriate one for the new calibration.
  3. Most software assumes the profile doesn't change, and checks the monitor profile only when they start, so you often need to exit and restart any program running that writes to the monitor before they notice the change of calibration.  Photoshop regularly checks the monitor profile, so you don't need to restart it.  Just do something that makes it re-render the image. 

Eizo has a utility called "Colornavigator" for their monitors which does both 1 and 2, but you still have to do 3.

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Simon

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