[Digikam-users] Color management behaviour

Gilles Caulier caulier.gilles at gmail.com
Mon Jun 22 11:13:25 CEST 2009


2009/6/22 Leonardo Giordani <leonardo.giordani at treuropa.com>:
> Francisco,
>
> thank you for you advices. I notice some inconsistency in color management,
> though. My issues happen if I click on my RAW picture and open it with
> "modify"; but if I use RAW importer as you suggested color management works
> as expected.
>
> Developers, something to say about this?

yes. Sound like something is broken in CM.

There are few entry in bugzilla about this subject. sound like code is
broken somewhere when port to Qt4 have been done.

I will review code before 1.0.0 final release. For the moment i'm busy
on other place (:=)))

Gilles Caulier

>
> Summary: opening a RAW data asks for "Assign" or "Convert" to workspace, but
> it works differently from how RAW importer works.
>
> Someone is experiencing the same issue (and the issues I talk about in my
> first mail?)
>
> Thanks
>
> Leonardo
>
> 2009/6/19 Francisco Lorés Ara <plores at telefonica.net>
>>
>> Hi Leonardo,
>>
>> I'm quite a newbie on color management, but I'll try to describe my setup
>> and workflow in the hope it helps you.
>>
>> I'm using an EOS 450D and digiKam 0.10.0 on openSuSE 11.1. The first thing
>> with CR2 files is that they don't have an embedded or built-in color
>> profile.
>>
>> But, we need to tell digiKam which is the camera profile. I've been
>> wandering a while with Digital Photo Professional (the raw converter/editor
>> supplied by Canon). At least in mine, the camera profiles can be found under
>> the folder
>>
>> C:\Program Files\Canon\Digital Photo Professional\icc
>>
>> There are in fact a pair of ICC profiles, one for sRGB color space and one
>> for
>> AdobeRGB color space, for each picture style available
>>
>> Faithful: fs.icc, fa.icc
>> Landscape: ls.icc, la.icc
>> Neutral: ns.icc, na.icc
>> Standard: ss.icc, sa.icc
>> Portrait: ps.icc, pa.icc
>>
>> So if you work with sRGB colorspace, the suitable camera profiles should
>> be fs.icc, ls.icc, ns.icc (*s.icc for sRGB), and so on. Copy them to
>> /usr/share/color/icc under Linux and configure the path and preferred input
>> profile on the Color Settings setup tab. These profiles are *not* identical
>> to standard sRGB or Adobe RGB, they are specific to the camera model. This
>> can be the reason you see the picture differently with/without color
>> management.
>>
>> As for the monitor profile, monitors come frequently with a "driver" in
>> CD, part of which is the monitor's color profile. For example, I own an LG
>> Flatron (not quite a good display as I would be pleased to have ;-) ). I
>> searched on the driver CD and found the file lh1970hr.icm, which is the
>> display profile for this particular model. As before, I copied this file to
>> /usr/share/color/icc and selected it in digiKam setup. And as before, the
>> monitor's profile is *not* identical to standard sRGB (although
>> approximate), it is specific to the display model.
>>
>> On the other hand, a distinction must be made between profiling and
>> calibrating a monitor. Both are **essential** to have a good, or at least
>> acceptable, color-managed workflow; otherwise you'll get under/overexposures
>> while adjusting, as well as color shifts/casts. So in addition to getting a
>> good monitor profile, you need to calibrate as much accurately as you can
>> the monitor's black point, white point, and gamma. I suggest the methods
>> described in the excellent tutorials and charts from Norman Koren at
>>
>> http://www.normankoren.com/makingfineprints1A.html
>>
>> which, if you don't need an extreme color accuracy, can be done "eyeball"
>> without the need of a spectrometer.
>>
>> Personally I always shot RAW in Adobe RGB colorspace, as it is a bit wider
>> than sRGB and well suited for editing / printing. On the RAW converter I
>> select the Landscape Adobe RGB input profile (la.icc) for general use, but
>> change it when appropiate (pa.icc for portraits for example).
>>
>> Once finished editing, I select Color -> Color Management, set Input
>> Profile = Embedded profile, Workspace profile = sRGB and click OK to convert
>> from Adobe to sRGB. Then I save the finished image in JPG or PNG format with
>> sRGB embedded in it. In this way I see the picture OK in digiKam as well as
>> in Gwenview or the GIMP.
>>
>> Maybe the camera profiles are different for your 350D, but you can install
>> Digital Photo Professional in a Windoze box, and use the filemon.exe utility
>> from Micro$oft
>>
>> http://technet.microsoft.com/en-us/sysinternals/bb896642.aspx
>>
>> to investigate which files are opened/used during conversion and editing.
>> One or more of them will be the camera profiles :-)
>>
>>
>> Wow, sorry for the length ;-) I hope that if something is wrong the
>> "gurus" will reply with the truth (don't forget I'm also a newbie :-)),
>> simply it works quite well for me.
>>
>> Regards,
>>
>> Francisco
>>
>>
>
> --
> Leonardo Giordani
>
> Tele-Rilevamento Europa - T.R.E. s.r.l.
> a POLIMI spin-off company
> Via Vittoria Colonna, 7
> 20149 Milano - Italia
> tel.: +39.02.4343.121
> fax: +39.02.4343.1230
> e-mail: leonardo.giordani (at) treuropa.com
> web: www.treuropa.com
>
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