On Saturday 05 August 2006 00:19, Frédéric wrote: > On Saturday 05 August 2006 00:35, Olaf Gellert wrote: > > [I'ill try to answer you, according to what I understand about color > management. I may do some mistakes, so please, wait for a guru answer ;o). > My answer is an exercise to me. My apologizes if there are mistakes]. > > > I am working on my photos (usually with GIMP) on a > > calibrated display (NEC2180 + Eye-One). > > You are using a calibrated display, but are you using Gimp-2.3, which > support ICC profiles for your display? > > > - Save the image with GIMP (as usual) > > - Use jpegicc or tifficc, using my monitor profile > > as input profile and the printer profile (given > > by my print service provider) as output profile. > > - send the image to the print service > > If you work with Gimp-2.3, then the image is edited in sRGB colorspace, but > correctly displayed in your monitor colorspace. So, source profile should > be sRGB, and destination profile the printer one.
I am not so sure that images in GIMP are "edited in sRGB colorspace" . I do know that versions of GIMP before 2.3 that GIMP were totally color management dumb and just assumed that all images were in the same unknown (unspecified) color space. In other words GIMP has always edited the image in what ever color space the image was in. All it does is manipulate the RGB values of the image regardless of what color space the image has. If the image is an sRGB image then the image is being edited in sRGB but if the image is in the ProPhotoRGB color space then it is not being edited in sRGB. > > If you are not using Gimp-2.3, then, yes, I think your are right, and you > have to use the monitor profile as source profile. No this is not correct. You need to use whatever color space is correct for the image. If you captured the image with a camera or scanner then you need to use a profile for that camera/scanner to either work directly in that color space or to convert the image from that color space to some standard working color space of your choice such as AdobeRGB, ProPhotoRGB, BetaRGB.... There are two open source options for creating camera/scanner profiles that I know of - AgryllCMS and LProf. Both have world class algorithms for creating these profiles and both run on *nix, Windows and Mac. LProf is easier to use and supports more input image file formats but AgryllCMS support hardware based monitor profiling and printer profiling. So all you need is a good IT8.7 target (I recommend those from Wolf Faust) and a little time and effort and you can create excellent custom profiles for your camera and/or scanner. If you do use a standard working color space avoid sRGB as it is simply too small to handle the gamut/dynamic range of most source material. This is particularly true for DSRL cameras where you process the raw data and for high dynamic range film scanners. Friends don't let friends use sRGB. To use your profiles in GIMP 2.3.x (I think the last development snap shot is 2.3.10) you need to trick it into doing the correct thing because the color management stuff is still not fully implemented. The trick is to set File => Preferences => Color Management => RGB Profile to whatever profile is correct for your image. Then set File => Preferences => Color Management => Monitor Profile to the monitor profile that you created using your i1 and it's software. At that point you will have a color managed display but you have to remember that GIMP currently does not know about or use embedded profiles and you have to manually set the correct profile in the RGB Profile field in the CM preferences. I have been using CinePaint more lately. It has full CM awareness (it knows how to use embedded profiles for example) and will handle images with higher bit depths (16, 32 bits/channel as well as images with float and double values). GIMP is currently limited to 8 bits/channel. The disadvantage of CinePaint is that it's tool set is somewhat limited. But it does have all of the basic tools you need for most things and if your work flow consists of making basic image adjustments (color balance, contrast, brightness, curves, levels...) and cropping then it will do the job very nicely. I always recommend that those new to CM have a look at Norman Koren's web site http://www.normankoren.com/color_management.html . It has lots of introductory material as well as lots of advanced information about how all of this should work. He has diagrams of the basic CM workflow that are very helpful to new CM users for example. The information is somewhat Windows and commercial software centric so if you are using open source software or are not on Windows you will have to take this into account. But in general the information is presented in a very accessible way. Hal ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
