Re: color management

[Felix Riemann <friemann svn gnome org>]

Hi!

On Sun, 2009-03-29 at 10:14 -0500, Leonard Evens wrote:
> It is my understanding that eog makes use of color management, taking
> information about the display from X.
> 

Yes, it tries to load the profile that's uploaded in the _ICC_PROFILE
property.

> I am running Fedora 9 Linux, and I've calibrated/profiled my display
> using the argyll collection of programs.   I've loaded the profile into
> X, and indeed xprop -root | grep ICC shows it is there.
> 
> gimp makes use of this information as does the program inkscape, and
> images are displayed exactly the same in both programs.  But eog shows
> the same image that gimp and inkscape do when I turn off display color
> management.   Also, if I remove the display profile from X, and then
> load it, what eog shows is unaffected.   It is, of course, affected by
> loading calibration vlut information into the video card.
> 
> I've been using eog 2.22, but I recently compiled and installed 2.24 and
> the result is the same.  Under Fedora (, it would require too much
> additional effort to compile and install version 2.26 because I would
> have to upgrade other components of the system.
> 
> I scanned the source code for icc, and although I didn't try to follow
> exactly what the code does, it does apparently try to make use of the
> profile in X, as best I can tell.
> 
> Can you explain what is going on.  Should eog include under preferences
> a choice of turning on color management as other applications do?
> Sould I have compiled it with appropriate options?
>  

Okay, first check if eog is compiled with ICC support (Fedora's packages
are IIRC), e.g. by checking configure output or checking if the binary
is linked against liblcms.so.

Then, eog is also very picky about when to apply the profile. It only
supports color correction for JPG and PNG files using the RGB pixel
format. Then the image needs to either have an ICC profile embedded or
have some metadata tags which say that it's sRGB. Some PNG files also
carry chromacity and white point information which can be used by eog to
create a matching profile. eog is not yet making the assumption that an
image without a profile is in sRGB as GIMP does.
Some reasons for this are we don't support extracting profiles from
formats like SVG and TIFF, and that we get the image data in either RGB
or RGBA  (colorcorrecting RGBAs eems to be a story of its own) from the
gdk-pixbuf library (which does the decoding for us) among other things.

Hope that helped you a bit,

Felix