Re: Color management in ubuntu

[Pascal de Bruijn <pmjdebruijn pcode nl>]

On Thu, Jul 1, 2010 at 7:29 PM, Pascal de Bruijn <pmjdebruijn pcode nl> wrote:
> On Thu, Jul 1, 2010 at 6:18 PM, Marek Matulka <marek matulka gmail com> wrote:
>> Hello,
>>
>> This is my first post on the group, but I've been following a group for
>> some time. Well done guys for a rocking bit of software giving us a
>> great colour management tool!
>>
>> On Thu, 2010-07-01 at 17:58 +0200, Pascal de Bruijn wrote:
>>> > 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.
>>
>> I had similar issue - when I created three images: 1. tagged with Adobe
>> RGB, 2. tagged with sRBG, 3. untagged - all three images were correctly
>> displayed in GIMP, but not in any desktop viewer.
>>
>> I think the problem lies in assumption, that for untagged images viewer
>> should not apply monitor profile, while it should assume sRGB and
>> convert it accordingly. It seems GIMP is working that way hence all
>> three images are correctly displayed.
>
> The tagging of an image has _NOTHING_ to do with applying a display
> profile or not... If this really is the case, then someone should
> really be shot for that (not dead... the knees will do just fine :).

Cutting my own rant short...

It's easy for forget (I often do), that color management as a concept
is non-obvious for pretty much everybody (including normal coders) who
aren't into this stuff...

Regards,
Pascal de Bruijn