[Digikam-users] Jpeg export changes image

[Hal V. Engel]

On Friday 19 October 2007 02:01:37 Guillaume Castagnino wrote:
> Le vendredi 19 octobre 2007, Arnd Baecker a écrit :
> > Hi Bill,
> >
> > I think that your question is related to this wish,
> >   http://bugs.kde.org/show_bug.cgi?id=142055
> > but I might be wrong.
> >
> > Guillaume, maybe you can explain things? ;-)
>
> Hi,
>
> No I don't think help here.
> The problem encountered by Bill here is probably the lack of color
> management profile that impacts the color rendering far more than (in
> fact more acuratlly) setting a right color balance or an auto exposure.
>
> Currently, the raw converter in 8bits will do auto-exposure of the raw,
> so it's not problematic, the "lights" will be correct
> My patch will help setting more preciselly the raw white balance.
>
> But IMHO, the problem that bill have here is some wrong color rendering
> more than exposure or white balance. A color managed view will change
> in a non-linear way the color balance of the picture.
> Look here for example, and especially the pictures on the right :
> http://ufraw.sourceforge.net/Colors.html
> Some colors have a big change (look especially at the purple balloon,
> the pink shirt, and the yellow trousers), this is what color management
> do : some color are renforced, some other are attenuated, and so
> picture saturation can greatly change, in order to better fit the real
> colors (profile depending on the camera used).
>
> For the story : I generally get the same pale result without using any
> color profile with my Canon 400D. Using the right color profile solves
> those color fidelity problem :)
>
> Regards,
> Guillaume

I would agree with Guillaume this is a color management issue or rather an 
issue with not having color management setup correctly.  It is now fairly 
simple to create high quality camera and scanner profiles with minimal cost 
using open source software.  All you need is a good profiling target.  IT8 
targets are available from Wolf Faust for very reasonable cost (an A4 target 
is $40 including shipping to the US and are even less in Europe).  For 
software you have two open source options.  ArgyllCMS and LProf.  In general 
you will likely find LProf easier to use and that it will produce very high 
quality profiles for your cameras and scanners.   Both sets of software also 
support display calibration and profiling with a number of commonly available 
measurement devices.

Hal