Color distortions in color managements applications

[Sven-Kristofer Pilz]

Hello fellow ColoHug users.

I see strange color distortions in applications with build-in color
management, attached is a screenshot of gimp showing a blue image. If
the color management of gimp is activated, the blue (0000FF) is
transformed to 5500D0. But only in the canvas, the preview in the tab
and the color picker still show blue. Eye of GNOME and Chromium also
transform images in that way.

The profile is https://icc.opensuse.org/profile/58657477a87c682f8200000a
and was created with DisplayCAL.

Any idea what is going on? Thanks.


Sven

[Richard Hughes]

On 29 December 2016 at 21:08, Sven-Kristofer Pilz <sven...@gmail.com> wrote:
> The profile is https://icc.opensuse.org/profile/58657477a87c682f8200000a
> and was created with DisplayCAL.

That's a pretty big color shift. Are you loading the color profile
gamma ramps with GNOME? Looking at the profile it's not insane so I'm
a bit confused why the blue is so wrong; one thing to notice was the
VCGT seems to bottom out at near zero values. When you calibrated, did
you perhaps calibrate with a very low brightness set? The CH2 is
capable of reading very low light levels, so I'm grabbing at straws a
little.

Richard

[Graeme Gill]

Sven-Kristofer Pilz wrote:
> I see strange color distortions in applications with build-in color
> management, attached is a screenshot of gimp showing a blue image. If
> the color management of gimp is activated, the blue (0000FF) is
> transformed to 5500D0. But only in the canvas, the preview in the tab
> and the color picker still show blue. Eye of GNOME and Chromium also
> transform images in that way.

Hi,
the colors are being transformed in a way that is
consistent with the profile you are using. i.e. sRGB pure
blue 0000ff maps to 5500D0 through your display profile cLUT.

Looking at your profile gamut surface compared to sRGB, it
appears that the blue primary is very much greener than
sRGB, and the overall gamut is smaller. If this doesn't seem
to match what you expect from your display, then I would
suspect that your ColorHug is not giving very accurate
measurements, although the only way to be sure of
that would be to compare the primary readings to
those from another instrument (i.e. say an i1d3).

Cheers,

Graeme Gill.

[Sven-Kristofer Pilz]

It seems that profiles generated with colord+colorhug don't have these effects,

but they don't look as good as those generated with DisplayCAL. Do the profiles

generated with colord not contain the cLUT? Can the cLUT be removed from those

generated with DisplayCAL? Does this question even make sens? :)

Thanks.

[Graeme Gill]

Sven-Kristofer Pilz wrote:
> It seems that profiles generated with colord+colorhug don't have these effects,
> but they don't look as good as those generated with DisplayCAL.

I'm not sure what you mean by "don't have these effects". Perhaps it
would be more obvious if I was able to look at the two profiles in question.

If they are substantially different (i.e. primary colors), then that
would hint that the instrument calibration being used by colord and ArgyllCMS are
quite different.

> Do the profiles
> generated with colord not contain the cLUT?

Perhaps Richard can answer that, since I'm not clear what code
generates the profiles via colord.

> Can the cLUT be removed from those
> generated with DisplayCAL? Does this question even make sens? :)

Using ArgyllCMS/DisplayCAL you should be able to set the type of
profile created, i.e. see <http://www.argyllcms.com/doc/colprof.html#a>

Cheers,

Graeme Gill.