Re: Color management in ubuntu

[Pascal de Bruijn <pmjdebruijn pcode nl>]

On Thu, Jul 1, 2010 at 5:31 PM, Gys van Zyl <gysvanzyl gmail com> wrote:
> Hi all,
> I have a couple of questions that may be a bit silly due to my beginner
> level knowledge of color management.
> I'm an amateur/hobby photographer and I've been using ubuntu for a while
> (currently using 10.04).  For a while now I've realized the importance of
> having a color managed workflow, but have put off getting the hardware as I
> thought getting everything installed, set up and configured would be tough
> in linux.  I recently purchased a Pantone Huey monitor calibration device
> and you could imagine my pleasant surprise when I found how extremely easy
> everything was to use with gnome color manager.  In no time, with almost
> zero effort I had everything up and running.  Kudos to the developer(s) -
> this is excellent software!

GCM + Argyll is a powerful combination indeed :)

> So, to test how color management works in a browser, I found this web
> site: http://www.gballard.net/psd/go_live_page_profile/embeddedJPEGprofiles.html.
>  Using google chrome (a non color managed browser) this page is a mess of
> incorrectly rendered photo's - I expected this.  Using Firefox, things are a
> lot better - imbedded color profiles are now honored and the photos display
> fine. However, about half-way down the page at the heading "sRGB / Standard
> RGB 2.2 gamma" I've come across a problem.  This photo is a tagged/untagged
> rollover of an sRGB image.  It says that "If your monitor is profiled to 2.2
> gamma and D65- 6500 kelvin, there should be minimum change in the Un-tagged
> sRGB rollover."  In my Firefox window, the change is not minor, and I'm
> trying to figure out why this is.
> In my workflow all exif data is stripped from my photo's before I upload to
> the web.  I thought that this wouldn't matter, as long as my final image was
> created in an sRGB colorspace.  However, I have now found that my photo's
> look subtly but definitely different in the software I use (gimp, digikam)
> and my browsers.
> My limited understanding of color management led me to believe that
> un-tagged sRGB images should look the same in a browser on a color-managed
> system.  However, on my system they don't and its causing a problem for me -
> my photo's don't display the way I intended.  How can I resolve this?  Is my
> understanding wrong, should I educate myself a bit more?  Did I do something
> wrong when I calibrated my monitor?

The problem is that being color managed, and being properly configured
is not always the same...

All color managed applications checked for an embedded profile when
loading images and will for example convert an Adobe RGB image to sRGB
on request. If an image is untagged sRGB will be assumed.

However, if you do not properly configure the application to use your
display profile it will be displayed as plain srgb without your
display profile applied, hence wrong colors (since only the videolut
will have effect).

I think GIMP doesn't use the system display profile by default.

Firefox also requires the display profile to be configured through
"about:config" search for "display_profile".

Same goes for lots of other applications. So you will still need to
check each an every applications configuration. Since they might use
poor defaults.

Regards,
Pascal de Bruijn