On Sat, 2008-04-05 at 17:46 +0100, norman wrote: > < snip > > > > It sounds like some color management problem, but I'm not sure exactly > > what. To start, have you profiled your monitor? Are you choosing a > > profile in gimp? The image viewer almost certainly is not using any > > profile information except thaqt which may be loaded into the video card > > memory. Gimp may be doing something different. > > I have not profiled my monitor and I am not choosing any special profile > in GIMP. Is it complicated to profile a monitor?
Profiling a monitor can be fairly complicated. You can find a general discussion of it at www.normankoren.com/color_management_2A.html. It involves two steps: calibrating the monitor thru hardware controls, and adjusting what is sent to the monitor from the RGB values in the image file, ie.e. the color balance of the image as it appears on the monitor. You can do a basic calibration by setting contrast and/or brightness (depending on whether the monitor is a CRT or LCD) and then setting gamma using images on Koren's web site. (See also www.cs.cmu.edu/~efros/java/gamma/gamma.html.) You can set the gamma under Linux using either xgamma or xcalib. The second part of the proces involves color profiling, for which you really need a device such as the Eye One Display or better the Eye One Pro. the latter is much more expensive but also allows you to profile your printer. Under Linux, you can both calibrate and profile your monitor with such a device using the program lprof or using the argyll suite of programs. The latter can also do your printer if you have the right device. Lprof may be already available as a package under ubuntu; it is under Fedora. The argyll suite must be donwloaded. The documentation is pretty clear, but it must be read very carefully, and you have to know what the words mean. It also has a very active users group which can be very helpful. Try googling "argyll color management" for more information, But I should warn you that the learning curve for these tools, and for color management in general is very steep. If you are determined to understand it, you should start with Norman Koren's web page, but you would be well advised to study a book like Real World Color Management. It covers the basics very well, but most of the book assumes you are using commercial software available under Windows or MacOS. Some of this can be adapted to Linux, but you it is hard to dig out just that part. I've been working on understanding color management for many months, and I don't think I've completely mastered it yet. Unfortunately, the gimp manual documentation on the subject is pretty sketchy and some of it, I think, is misleading. I suggested some improvements to the gimp-doc group, but the last time I looked, they had not been adopted. You should probably do a minimal adjustment for gamma, as described on Norman Koren's web page, but you will probably find it doesn't make much difference. The default calibration and profile---sRGB---is probably not that far from what careful profiling would yield. I suspect that this is not the problem in your case. As I suggested earlier, it sounds as if the image viewer and gimp are using different profiles or assuming different color space models, which amounts to the same thing. It is remotely possible that ubuntu has added some color profiling to its interface, but I really doubt that. Gimp will by default use sRGB, which is supposed to be an average profile for monitors, and the image viewer is probably also using it. If a profile for a color space is embedded in your image file, gimp may be choosing that instead, and then what it shows will be different from what the image viewer shows. You can check that by using Image properties>Color Management in gimp. Also, just what gimp will do with an embedded profile it finds in an image is determined under Preferences>Color Management. > > Norman > _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user