I am trying to use color management under gimp 2.4. Despite numerous google searches and posting to the gimp user group forum, I've been unable to find any useful documentation about how to use it. Through trial and error and many hours fumbling around, I've managed to decipher much of it, but I'm still unclear on some points.

How to use the display profile was fairly clear. Profiles for input files was very murky, but I eventually worked out what was happening there. One confusing thing was that if you specify in Preferences>Color Management that gimp Keep the embedded profile, the same thing happens---i.e. no indication---if that profile is the same as the default sRGB profile or if there is no embedded profile, so you can't tell at that point whether or not the source file had one. With some searching I eventually found a couple of other places where that information is provided. I don't suppose it really makes any difference, but it was thoroughly confusing to me.

I think I understand generally how to do print simulation, but some points are unclear. Under Preferences>Color management>Print simulation profile I specify a printer profile, and I then choose Mode of operation to be Print simulation. If I check the Mark out of gamut box, then it shows me colors that are not printable. If I don't check that box, I see various colors and I'm assuming that these are roughly the colors as they will be printed. That of course depends on the rendering intent which together with the profile should determine how colors are transformed so that everything ends up in gamut.

Have I got that right so far?

One thing that confuses me is that I can either choose Color managed display or Print simulation as the Mode of operation, but not both. It doesn't seem to make sense for print simulation to ignore the display profile, but perhaps I am not understanding something.

I am completely at sea about how I use the print profile to actually print. Do I set the mode of operation to print simulation and then choose print from the file menu? Or do I put the print profile in the RGB profile slot and then print? Or is this as yet unavailable and dependent upon adding profile capability to gimp print or gutenberg?

Finally, I am unclear where else in various gimp menus and tools, color management shows up either in making choices or in providing information. If there is any other useful information about gimp color management that anyone can provide, I would appreciate it.

On Mon, 2007-12-24 at 14:30 +0100, Sven Neumann wrote:

I am completely at sea about how I use the print profile to actually print. Do I set the mode of operation to print simulation and then choose print from the file menu? Or do I put the print profile in the RGB profile slot and then print? Or is this as yet unavailable and dependent upon adding profile capability to gimp print or gutenberg?

Printing is usually left to professional print services and they should do the right thing if you give them an RGB image with embedded color profile. If you print from within GIMP, there isn't any color management support yet.

Thanks for the information.

I'm afraid I have two additional questions.

First, do you have any suggestions at all about what I might do if I want to print with my own printer for which I have a profile? Since most users of gimp probably want to do just that, it would be very helpful if there were a way to do it. The only way I can think of is to boot Windows XP and use Photoshop, which I would rather not do.

Second, I'm not sure I understand what gimp embeds in a saved file. I've done some experiments, and the results are confusing. Let me describe what I found. It is a bit long winded so bear with me.

I scan using vuescan which allows me to specify the output space and puts the appropriate profile in the tiff file it produces. When I specify sRGB, then gimp keeps that profile since it is the default. If I save that file, then iccdump does in fact find that embedded profile in the resulting file.
But if I specify another output profile in vuescan, e.g., Adobe RGB, gimp converts to that as expected. (I verified that using Image>Properties>Color Profile.) Now, if I save that image iccdump apparently locates a profile, but then issues the error message

Error - 1, icmHeader_read: ICC V4 not supported!

I have the same problem if I specify in gimp under Preferences>Color Management>RGB Profile some other profile and specify File Open Behavior>Convert to RGB Workspace.

I appreciate that this is a problem with iccdump, but it seems clear that gimp is doing different things depending on whether or not the profile is the default RGB profile. Can you explain why? Also, do you happen to know of any other program to detect an embedded profile which does support ICC V4?

Sven