[Gimp-user] Color profiles & color spaces -- assignment v. conversion?

[Hedley Finger]

David, Sven:

> On Thu, 2008-07-17 at 16:52 +1000, Hedley Finger wrote:
>   
>> I know just enough about colour management to get myself into trouble.
>>
>> On Gimp 2.4.6, there are now some new options under the Image > Mode >
>> menu path, namely
>>
>> @   Assign to Color Profile // Actually uses Little CMS (lcms)
>> @   Convert to Color Profile // Actually uses Little CMS (lcms)
>>
>> @   Assign colorspace  // Hmmm, should be 'Color Space' for niceness?
>> @   Convert colorspace  // Likewise!
>>     
Sven replied:
> If you see four options there, then you have installed some additional
> third-party plug-ins for color management that you should not need with
> GIMP 2.4. It's probably best to get rid of those extra plug-in(s).
>   
Yes, a respondent on another list said something similar -- the last two 
options were probably inherited from a previous Gimp 2.x release, 
because the Windows installer by default installs into the c:\Program 
Files\Gimp-2.0\ folder created by previous installers.  The first two 
options actually call Little CMS to do the work.
>> @   What does *assigning* an image to a colour profile do and what
>> effect does it have on colour management downstream?
>>     
> It changes the meaning of the pixel values. Generally this means the
> image looks different.
>   
David, I see no difference when importing an image with no 
attached/assigned profile.  But you are saying that the pixel numbers do 
not change, so no harm done if an inappropriate profile assigned -- just 
assign a more appropriate one?
>> @   How is *converting* an image to a colour profile differ from
>> "assigning", and what effect does it have on colour management downstream?
>>     
> Converting, instead of assigning a different meaning to pixel values,
> converts the pixel values from the previous color profile to the
> profile you specify, so that the result is as close to identical as
> possible to the original..
>   
So this is an irreversible step -- you may not be able to convert back 
to a previous profile because the pixel values may not contain enough 
information to allow this to happen?

Regards,
Hedley

--

Hedley Finger

28 Regent Street   Camberwell VIC 3124   Australia
Tel. +61 3 9809 1229   Fax. (call phone first)
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Email. "Hedley Finger" <hfinger at handholding.com.au>

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