[Digikam-users] Printers with full Color Management

[Gerhard Kulzer]

On Friday 04 September 2009 09:47:24 pm Milan Knížek wrote:
> Marcel Wiesweg píše v Út 01. 09. 2009 v 19:49 +0200:
> > > camera icc profile prepared for Adobe Lightroom will most probably
> > > provide different colours in UFRaw. Not saying worse or better, but
> > > different. But yet - if you do not have anything better and are happy
> > > with the result, do not worry.
> >
> > The part about the printer is clear to me, but where is the difference
> > for RAW files? I see there can be differences in RAW development -
> > demosaicing algorithms etc. - but once you have your colors in
> > uncalibrated color space, applying the color conversion using the input
> > color profile should be the same?
> 
> I cannot provide much technical details at this area, just a laic
> understanding of the information available on ufraw and argyllcms
> mailing lists...
> 
> AFAIK, the thing is that not all converters apply the same steps in the
> same order and that some of the steps are variables affecting the raw
> and rgb data. Some of the settings can be set by the user, some may be
> hidden (and proprietary).
> 
> E.g. UFRaw applies white balance, highlight-reconstruction, wavelet
> de-noising, raw curve adjustment, gamma and linearity before 
assignment
> of the camera profile.
> 
> Next problem is that the camera sensor does not react fully linearly to
> the light - hence an icc profile prepared for a particular
> white-balance/raw curve/etc. and used for another
> white-balance/curve/etc may provide different result even in the same
> raw converter.
> 
> If my understanding is wrong, I would be more then happy to know other
> opinions.
> 
> P.S.2 The difference is quite obvious when using Canon's Digital Photo
> Professional and UFRaw. There are methods how to find out, which ICC
> profiles are used by DPP in MS Windows. However, people were usually 
not
> able to get the same output from UFRaw with those profiles. (I tried
> myself and skipped this approach - the Adobe Matrices in dcraw based
> converters provide better results).
At least theoretically you are wrong in the sense that color management 
should be independent of MS or Linux or whatever, it's the very sense of it. 
CM transforms an image from one color space into another by transiting 
through an ideal color space, it's a mathematical operation not dependent 
on any drivers.
But then there is the question as to whether the CM has been correctly 
implemented by a specific program or driver.  

I've been trying to find out what profile Canon is using in DPP for my 30D, 
then 40D and 50D. For the 30D I could track that DPP loaded a certain 
profile, but for the 40D and 50D DPP doesn't seem to load any profile, it's 
built-in. I've tried all profiles delivered with DPP on Linux with UFRaw and 
digiKam - none of them gives the same results than DPP, unfortunately. I 
believe Canon is playing games with us, they use their own "kitchen" and 
don't give it away. I believe (and I haven't pursued that allay yet) the two 
only ways to get a profile for the latest Canons are 
1. doing your own profile, 
2. Look into what Adobe is doing in their Raw converters. 

Gerhard

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