[argyllcms] Re: The different color temperatures: questions: Please look again!

Leonard Evens wrote:

I am still a bit unclear about just exactly what happens in the monitor.

With the usual method using argyll, there is a vcgt tag which is loaded
in the video card.   I checked the default .icm file that came with the
monitor and one I made using the Huey under Windows.   (I did it in
custom mode, which was presumably wrong, but that doesn't matter for
what I say below).  Neither of these had a vcgt tag.   I presume this
means that what would normally go in that tag is (semi-)permanently
stored in the monitor and I don't get to see it.   Presumably the
two .icm files are meant to be used by Photoshop and other color aware
applications in the usual way.

Do I have that more or less right?


Yes.


If so, using argyll under Linux,
assuming I can skip making the vcgt tag, I can produce a profile and be
in business.
Yes (you have to invoke targen, dispread and colprof one after another to do so). 

Or you can simply copy the NCE profile to Linux.
Or you can use dispcal as usual (but skip the adjustment of the monitor controls) to fine-tune the NCE calibration results as Gerhard recommended. 


By the way, The profiles appear to be matrix profiles.   At one time, I
understood exactly how they work, but I can't remember the function of
the TRC part of the profile.  As a mathematician, I have no problem with
the matrix part. 

The TRCs map the calibrated device RGB values to linear RGB:

linearR =   redTRC[deviceR]
linearG = greenTRC[deviceG]
linearB =  blueTRC[deviceB]
This is the first step of the forward conversion (deviceRGB -> linearRGB). The linear RGB values will them be transformed to the profile connection space XYZ with a 3x3 matrix (linearRGB -> XYZ): 

p = Ar

p: XYZ column vector (Profile Connection Space)

          | rx, gx, bx |
A: matrix | ry, gy, by |
          | rz, gz, bz |

r: linear RGB column vector

The transformation is invertible by implication.

Klaus

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