[Digikam-users] Some color management questions

[Milan Knížek]

Rainer Krienke píše v So 13. 06. 2009 v 13:35 +0200: 
> Hello,
> 
> i run digikam 0.10 on my openSuSE 11.1 box. All my photos are in sRGB 
> colorspace. JPG files I convert from my cameras NEF files (using bibble) are 
> also in sRGB. In digikam colormanagement is disabled. So far so good. Up to 
> now I never had any color problems.
> 
Assuming your display device has a similar colour characteristics as
sRGB, this is really the easiest way to go.


> I looked at the photos XMP metadata where I found a Photoshop section. In this 
> section there is an entry "ICCProfile" with a value of "Adobe RGB (1998)".
> 
> - Does this mean that color in these JPGs is in Adobe RGB 1998 and not in 
> sRGB? If yes then perhaps this difference in colorspace could be the reason 
> for the pale colors, couldn't it?
> 
Yes. 
> - What should digikam actually do with a photo that is in Adobe RGB color 
> space?  Would it be automatically convert it to sRGB when I look at it? Do I 
> have to activate colormanagement in digikam to get things right even if I just 
> want to look at these photos?
That's a question. There is a setting to automatically convert to the
working colour space or to ask the user. I would prefer to have another
option - to preserve the image's colour space as is without asking. 
> 
> - Can a JPG actually contain an image in Adobe RGB or is (or should be) the 
> colorspace by definition sRGB in all JPGs? 
> 
JPEG can contain data in various target colour spaces - that depends on
user. To let the application know, what is the colour space, the icc
profile can be either embedded in jpeg (which make the file bigger), or
various tags can used for the standard profiles (exif.colorspace,
jpeg.colorspace). This information can be even conflicting and the
standard sets precedence of the data (which should be used in preference
before others).

You can use exiv2 or identify from ImageMagick to find out the details
(command line programs).

$ identify -verbose image.jpg
or
$ exiv2 -pa image.jpg

> I am actually unsure if I really have a color problem or if everything is the 
> way it should be, but since my friend does not live next door I cannot just 
> take a look on his monitor to see if he intended this "special" color look.
> 
Well, I have just started with digiKam recently so I am not fully sure how the colour
management implementation is supposed to work there.

So far, when comparing image displayed by colour managed CinePaint or
GIMP and digiKam (Image View, Image Editor) looks different. It might
be worth going through the documentation and reported bugs to find out more.

br,

Milan Knizek
knizek (dot) confy (at) volny (dot) cz
http://www.milan-knizek.net - About linux and photography (Czech
language only)