Getting good previews from color management depends on these steps from the user:
Having accurately profiled input devices which create the images. Scanners, digital cameras etc. Further on, the specifics are spelled out under tools. Most importantly an accurately calibrated and profiled monitor.
The first suggestion is to ease up on the eye candy. You might want to switch to or come up with a "vanilla" theme setup. Yes, KDE and Gnome have gorgeous desktops, but Scribus will like plain and simple - no animation, no fancy graphics. For the most accurate color calibration set your desktop to a neutral gray or light color with no gradients or fancy backgrounds. This will help your eye to better judge color balance for images. The same applies for the Gimp or other image programs. When I color calibrate monitors for Photoshop with a (expensive) hardware devices, this is the first step I make. What we are striving here is to accurately, as possibly, mimic the the way mixed inks look on paper.
Calibrating is setting the monitor to a known state. Most monitors are set to a default to color temperature of 9300k or Kelvin, which is often too "cold" or bluish for accurate color work. www.color.org has a multitude of color specs for your reference. Most color standards are set to 5000k light temperature or "illuminant". For your monitor, I suggest 6500k, which more closely mimics natural sunlight, as a starting point adjusting for your monitor. At first your eyes will think your monitor has a yellowish cast, but your eyes will soon adjust, especially if the brightness and contrast are set properly. 9300K, which is the default factory setting for most monitors is fine for working with a word processor, but this will wash out colors and color will look less balanced with whites actually showing a bluish cast.
Each of the "working" spaces are based on certain settings for your monitor. Gamma and color temperature of your monitor should match the specs of the working space. For example, Adobe® RGB and Bruce RGB specifies 6500k and 2.2 gamma, quite common for Intel based PC monitors and are the recommended defaults for users who are editing color critical images.
Targeting the CMYK device (the printer) properly using a profile, which is appropriate for the paper and device. Printer profiles are highly dependent on the media chosen. Newsprint and un-coated stocks are grayer in appearance, so these profiles will have a narrower "gamut" or color range. They do not to produce the super vivid colors and saturation of coated stock or glossy photographic papers. A single printer could have a half dozen or more profiles, based just on differences in the paper color and ink absorbency.
So, how do I get profiles which are meaningful for my hardware.?
Some profiles are "generic" and can be obtained from the device manufacturer. This type of profile is generated from a sampling of units by a manufacturer. A growing number of monitors, scanners and certain printer vendors will include this with any software bundled with the device. While these "canned" profiles are rarely a perfect match, this is a good first place to start. Go to the vendors website under drivers and see if there a profile available for your device. Another type of profile is a "generic" press standard profile. These are CMYK profiles which are defined to commercial press industry standards, such as SWOP, FOGRA, ECI and other print standards bodies.
Linux Color Tools
Monitor Gamma - Gamma simply put is a number which represents the brightness of neutrals or grays. Having Gamma accurately setup is an important first step in getting good color balance before trying to creating an accurate profile. The monitor profiler from littlecms is well designed to help you set this correctly.
The next step is in accuracy is a custom generated profile created with profiling software, like the ones in the the littlecms profile constructor set. See the instructions for profiling your monitor for details. It was interesting to see how similar the profile was to one created with professional pre-press color calibration software and a hardware tool under Windows 2000.
The most precise way to profile a monitor is with a electronic profiling device, basically a very special type of camera which measures color. The software sends known reference colors to the monitor which then read the output to the profiling device and creates a profile. Linux drivers for common "spiders" or colorimeters are not yet available, but the profiler can use hardware when device drivers are written. Users who have created custom profiles with a "spider" under Windows, might have try using this same profile if the monitor is set up exactly as in Windows AND if the Linux video driver does not make any radical adjustments to the color values of your display. It is worth trying at least! My "spider" created monitor profile works very well with Scribus. With color management activated, the colors within Scribus are just about exactly the same in Photoshop 6.0. Quite an achievement by both Scribus and littlecms!
Scribus Color Management Settings
System Profiles - These drop down boxes show the available profiles on your system. To enable Scribus to use profiles, they should be copied to the
$prefix/share/Scribus/profilesdirectory or you can put them somewhere in your home directory and point to this directory in your preferences.. Color profiles, .icm and .icc, are platform independent, thus files created or available for a Mac or Windows are usable in Linux with littlecms in Scribus, as well. See the links page for more info where to obtain profiles. I highly recommend having the Adobe profiles which are shown on the links page if you plan to do an type of cross platform or commercial printing, as most well set up DTP workstations, as well as most commercial printers will be able to work with these profiles.
The above screen cap is a good starting point to explain the important parts of littlecms in Scribus. In this case, the images in the document have been created with a mid-range digital camera. The camera's itself performs come automatic color balancing and auto adjusts the output for the sRGB range or color space. So, leaving this within sRGB is a good choice. If the images came from a scanner, you would want to select the profile created with scanner profiling software.
Solid colors can be described within RGB (red green blue) or CMYK (cyan,magenta,yellow and K for black - these colors represent the four inks used in process printing or in color ink jets). In this case, we are using some basic RGB colors, which will be later "soft proofed" in the CMYK color space of the printer, which will be a commercial process known as US SWOP on coated paper to ensure rich and vibrant colors.
It is handy to give your device profiles some sort of short hand way of naming. For example the D226500mon.icm monitor profile is a custom profile created with Qmonitorprofiler with 2.2 gamma and 6500k temperature. The D is for daylight. Ambient light also affects your perception of color, sometimes radically with certain types of artificial light. The Sony 17 name comes from the description when the monitor profile was created with Qmonitorprofiler from littlecms.
Activate Color Management enables color management globally within the document. Scribus will remember the settings from file to file. Note: Saving and closing the file with color management on will slow them on reopening, as Scribus must not only open the files but the littlecms must reading and perform the corrections between the profiles. Color conversions make multiple floating point calculations for each color, so be patient. littlecms has to be extremely stable so far, with only a couple of small bugs for profile handling. There is a second check mark to simulate the printer on the screen. This tells Scribus and littlecms to do an on the fly conversion from the image color space to your monitor profile to simulate your chosen printer's profile. The check mark for Mark colors out of Gamut will show colors are warnings and might not not print accurately, based on the printer profile you have chosen. Typically, when colors are shown out of gamut, they will print darker, lighter or have a color shift when printing. The last option, Use Black Point Compensation, is a way to help rendering shadows within color pictures. Experimentation is needed to see if it improves your pictures.
Rendering Intents
The other puzzler for newcomers to color management is rendering intents. Your choice of rendering intents are a way of telling littlecms how you want colors mapped from one color space to another.
Perceptual - This rendering intent maps color "smoothly", preserving relationships between similar colors. This prevents "gamut clipping" with its potential loss of detail and "tonal banding" problems. Gamut "clipping" happens when two or more colors that are different in the input image appear the same when printed. Perceptual rendering intent makes small adjustments throughout the image to preserve color relationships. It sacrifices some precision of colors in order to ensure pleasing results. For photographic images and scans, this is usually the best choice for a default setting.
Perceptual intent will produce the most predictable results when printing from a wide range of image sources, for example, when printing RGB images on CMYK devices, or when trying to match CMYK devices that are radically different from each other. Consider this "foolproof" setting to be best for users who handle the wide variety of images that commonly enter large format printing facilities.
Saturation stands for logos, spot colors, etc. It tends to preserve the amount of or vividness of color. But it can make photos look ugly. If you were working with logos with a specific shade, saturation will bring better color matching, as far as you give more importance to the color that to the image.
Absolute Colorimetric: When a color is not printable within the "gamut "of the output device, this rendering intent simply prints the closest match. It reproduces in-gamut colors without compromise, as faithfully as possible. This produces the most accurate matching of spot colors. Unfortunately, it can also result in "gamut clipping" where two colors that are different in the original are identical on the print. White points are similarly clipped, then causing color relationship problems in the highlights of images. This type of clipping, and the resultant problems, typically make this rendering difficult to use with anything but spot colors. Some users will be disconcerted with a yellowish cast in their image, but this intent is measured in highly controlled lighting conditions with a D50 light box. This often has a "warmer" temperature than more typical viewing conditions. This rendering intent is almost exclusively used when a corporate logo or color must be matched exactly regardless of media. Kodak yellow would be a good example.
Relative Colorimetric: When a color is not printable within the gamut of the output device, this rendering intent prints the closest match along with an adjustment that maps white to the paper of the output. This mapping of "white point" prevents the problems of "Absolute Colorimetric" when images except spot colors are concerned. When producing color proofs on RGB ink jet printers, while simulating CMYK printing presses you can use this intent, if you know the intended precise profile. Users of Adobe Press Ready will understand this concept quite well. This approach works well when you have accurate embedded profiles (typically scanner or more rarely digital cameras.) in images being converted to CMYK space with printer profiles very precisely profiled with color measurement devices. This is most likely when someone has spent a lot of time and effort to finely calibrate and profile their equipment. It takes sophisticated ($$$) color calibration equipment to measure the printer under fairly well controlled conditions.
For Scribus users, there are a couple of options for printing with a color managed intent.
When printing, Scribus can optionally apply the printing profile you have chosen in the color management panel. This can be very useful, if you want to simulate a commercial printer profile with your ink-jet printer via CUPS.
Postscript Output - This would require having your images tagged before being placed in Scribus files when outputting a Scribus document either: as pure postscript or as individual EPS files. Scribus uses level 3 postscript.Level 2 and Level 3 postscript can read and use icc profiles within an image. Most color postscript devices will read the embedded profiles and use them to render color within the postscript using something called a rendering dictionary.