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Colour space conversions in GIMP - how?

Jan 7, 2011, 13:43
Post: #1
Colour space conversions in GIMP - how?
Apologies first - just joined the form and posting a question already!

All I want to do is to
- convert some jpg pictures I took on my camera using (by mistake) Adobe RGB colour space.... (Camera is Nikon D5000 in case it's relevant)
- to sRGB then save as a TIF

I have experimented but am unsure of my results so here's the story:-
- I know GIMP is preloaded with sRGB colourspace
- I imported the Adobe RGB icc profile into GIMP and can see it in preferences so OK
- However I can ONLY see Adobe RGB in the dropdown, not sRGB so I found a sRGB icm and imported that into GIMP - now i can see both colour spaces and choose which GIMP should work in.
- I then tried opening one of my images, first setting GIMP space to sRGB and asking to be informed when loading a picture (that is not embedded sRGB)
- No dialog box came up, the image just opened. Looking at image properties, GIMP thinks the image is sRGB (why?)
- I then closed the image, changes GIMP's colour space to AdobeRGB and reopened teh image. Now GIMP thinks that the image is Adobe rgb
- I then did a conversion to sRGB using the supplied function in GIMP and the image became more saturated
- this may be Ok but I'm not convinced GIMP is doing teh conversion properly as

- it's not recognising the embedded colour space of an image - just opens it up as whatever colour space GIMP is set to
- where has the preloaded sRGB profie in GIMP gone - why did I have to load an external one?

Makes me feel all is not as it should be...

Many thanks for any insight into this!
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Jan 10, 2011, 13:17
Post: #2
RE: Colour space conversions in GIMP - how?
Well for those who are interested I have found the answers - quite revealing.

I downloaded a trial version of Photoshop and found:-
- Photoshop correctly identified the images as Adobe RGB
- I then converted to SRGB and saved as a TIF file.
- I then compared the converted Photshop image with the image I had converted using GIMP (where I had to first ASSIGN the Adobe RGB attribute to the image before converting to sRGB)

Result - the Photoshop and GIMP converted TIF's are IDENTICAL

That tells me that GIMP is capable of doing the correct colour space conversions BUT it is NOT colour space aware, you have to assign a colour space to am image first (assuming you know what it is to start with)

Hope that's useful to someone! Is this a Bug?
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Jan 10, 2011, 15:48
Post: #3
RE: Colour space conversions in GIMP - how?
You've read this?

http://docs.gimp.org/en/gimp-imaging-col...ement.html

Now answering your questions on
https://Gimp-Forum.net
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Jan 10, 2011, 16:50
Post: #4
RE: Colour space conversions in GIMP - how?
(Jan 10, 2011 15:48)ofnuts Wrote:  You've read this?

http://docs.gimp.org/en/gimp-imaging-col...ement.html

OK - Yes I did. The reason I suspect that there may be a bug is teh expected behaviour as described in teh acrticle do not happen - there was no dialogue box asking me if I wanted to convert themage to sRGB - looking at image properties, GIM thought the incoming image already WAS sRGB (it was Adobe RGB)

And I read in another tutorial somewhere that you have to load other colour spaces into GIMP as it only comes with sRGB - so i did this also to add ADOBE rgb.icc (which is how i can assign this colour space to the image before converting it to sRGB)
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Jan 10, 2011, 16:51
Post: #5
RE: Colour space conversions in GIMP - how?
Apologies for the awful typing above!
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Jan 10, 2011, 20:33
Post: #6
RE: Colour space conversions in GIMP - how?
(Jan 10, 2011 16:50)wp51 Wrote:  
(Jan 10, 2011 15:48)ofnuts Wrote:  You've read this?

http://docs.gimp.org/en/gimp-imaging-col...ement.html

OK - Yes I did. The reason I suspect that there may be a bug is teh expected behaviour as described in teh acrticle do not happen - there was no dialogue box asking me if I wanted to convert themage to sRGB - looking at image properties, GIM thought the incoming image already WAS sRGB (it was Adobe RGB)

And I read in another tutorial somewhere that you have to load other colour spaces into GIMP as it only comes with sRGB - so i did this also to add ADOBE rgb.icc (which is how i can assign this colour space to the image before converting it to sRGB)
The way I read it is that the image ought to come with its own colour profile if it's not sRGB. I think you stumbled upon an image in AdobeRGB without the attached profile, and that once you associated the right profile to it, it was saved with the image.

Now answering your questions on
https://Gimp-Forum.net
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