Re: Feature request: controlling the display white point

[Graeme Gill <graeme2 argyllcms com>]

Andrew Lutomirski wrote:
> One thing that's bugged my about both ArgyllCMS and g-c-m is that it's
> hard to set the target white point for the display.


Hi,
        perhaps you could explain how you think this could be
improve ?

Currently ArgyllCMS dispcal lets you set the white point as:

        Native (default)
        Daylight locus color temperature
        Black Body locus color temperature
        x,y coordinate

> 3. There are programs like f.lux [1] that vary the white point
> throughout the day.  I should be able to do this using tools like
> g-c-m.

Such "entertainment" programs are at odds with accurate reproduction
of color though.

> Ideally I'd be able to profile my display once
> (possibly in a slower mode that collected more data points) and then,
> whenever I want to set a white point, to generate the gamma ramp and
> profile for that white point on the fly.

While such a thing may be technically possible (and something like it
can be achieved using absolute colorimetric intent and color profiles)
the reason that ArgyllCMS colprof works like it does is in an attempt
to provide an accurate calibration by actually determining the
device values that meet the calibration target. It's not practical
to fully characterise a display - some level of sampling and
model fitting/interpolation is needed, and this introduces inaccuracy.
Such inaccuracy in profiling is reduced by having an accurately
calibrated device.

> From the colord/g-c-m point
> of view, being able to go into the g-c-m settings and select a white
> point for immediate application would be nice (and programs like f.lux
> could be replaced by some straightforward code to ask g-c-m or colord
> to change the white point).

It comes down to the mechanism being used for color management.
Ideally the calibration curves shouldn't be changed to achieve such
an effect, since their primary purpose is to improve the characteristic
of the device, not achieve color management (something they
are incapable of doing anyway) - if all the colors on the GUI were
being color managed, then you would instead just change the source
profile(s) being used for all the elements that you wanted to apply
this effect to, or interpose an an abstract profile in the CMM path.

Graeme Gill.