[Digikam-users] Showfoto and raw NEF files; Gamma and Linearity?

[Hal V. Engel]

On Sunday 28 October 2007 20:50:18 Ari El wrote:
> I've been using showfoto to do all my essential photo processing; I started
> to shoot raw in my nikon d80 and I'd like showfoto to do the raw conversion
> as well, since the recent versions do support color management.
>
> I've been playing with UFRaw and their posted D80 profile
> (http://ufraw.sourceforge.net/Colors/Nkx_D80_5_1691_06_000_434.icm), using
> gamma = 0.45 and linearity = 0 I get really good results (in the sense that
> it looks extremely similar to the cam's generated jpg)
>
> Now when I open the NEF with showfoto (ubuntu 7.10 / showfoto 0.6), i am
> presented with the color management dialog (or plugin); with it, I select
> the above mentioned input profile, and as workspace profile I select adobe
> rgb (same thing I do in UFRaw). However I can't find the way to set the
> gamma and linearity parameters in showfoto. The "target" displayed, and the
> result after I click OK, looks very different to the cam's generated jpg,
> with way too much color saturation.
>
> I guess I'm doing something wrong in showfoto here... can someone point me
> in the right direction?

In general you should be using a profile that was created for your work flow.  
That is different work flows require different profiles and using different 
software means that you are using a different work flow.  

My experience with my D70 using a custom profile in UFRAW is that the camera 
gamut is significantly larger than AdobeRGB-1998.  AdobeRGB-1998 has a gamut 
that is about 50% of Lab and my D70 has a gamut that is closer to 70% of Lab.  
So you will definitely loose some gamut and dynamic range if you do a 
conversion to a smaller color space like AdobeRGB-1998 at least for some 
images.  So you may want ot consider using a working space with a larger 
gamut. 

>
> ps. One thing I noticed is that, trying to set the default input profile in
> Settings > Configure Showfoto > Color management,  after I set the folder
> containing my profiles, the "Input" profile options listed include a few
> profiles I have in that folder but *none* of that folder's nikon profiles.
> For some reason my nikon profiles can not be set as the defaults. I can, as
> mentioned above, manually select the nikon input profile at the time I open
> each image.

The Nikon profile may not be correctly tagged as an input profile and smarter 
dialogs for presenting lists of profiles to users will use these tags to only 
show input profiles or display profiles or printer profiles when this is what 
is called for.  For example, the profile widgets in LProf for selecting 
proofing profiles do this.  So I would not be surprised if showfoto did this 
as well.

Marti Maria, the author of LCMS, estimates that as many as 25% of the profiles 
out in the wild have at least something that does not meet the ICC 
specification.  Perhaps your Nikon profile is one of these.