Posts Tagged ‘color management’
To calibrate a monitor and generate a color profile for it on Linux, you need two things: a colorimeter and color profiling software. High-quality professional colorimeters tend to be rather expensive, but you can use the excellent open source ColorHUG device instead. When it comes to calibration and profiling, the displaycalGUI software is the perfect software for the job. It provides a graphical user interface to the display calibration and profiling tools of the Argyll CMS open source color management system. The latter is available in the software repositories of most mainstream Linux distributions, so you can install it using your distro’s package manager. On Debian and Ubuntu-based distributions, this can be done by running the apt-get install argyll command as root. Grab then the packaged version of dispcalGUI from the project’s website and install it on your system. Connect ColorHUG (or any other supported colorimeter) to your machine and launch dispcalGUI.
Press the Refresh button to make dispcalGUI detect the connected colorimeter (it should appear in the Instrument/Port section). If you are using a multi-display setup, make sure that the correct monitor is selected in the Display device section. Select then Photo from the Settings drop-down list. Press then the Calibrate & Profile button and follow the instructions to calibrate the monitor and generate its color profile. Once the color profile has been generated, dispcalGUI prompts you to install the profile and enable it during boot.
Launch then digiKam, choose Settings → Configure digiKam, and switch to the Color Management section. Click on the Profiles tab, select the generated profile from the Monitor profile drop-down list, and press OK to save the settings.
First of all, what’s color management? Color management is a process that allows you to achieve consistent color representations across different devices, such as digital cameras, scanners, printers, and monitors. The key concept in color management is color space — a model that describes the way colors can be represented as numbers. The Dry Creek Photo page explains it best:
A color space provides the definition for what color the numerical combination represents. Color spaces are akin to languages. A value such as 88/249/17 is given meaning by the color space in the same way as an otherwise random sound has meaning in a particular language. If our example of 88/249/17 is interpreted using the Adobe RGB color space, it is a vibrant, attention getting green. If, on the other hand, the same value is interpreted using the sRGB color space, it is a pale, sickly yellowish-green.
In most cases, you don’t have to worry about color management (see Ken Rockwell’s explanation why color management is a non-issue for most photographers). But if you do need to take control of colors, digiKam’s got you covered.
To enable the color management feature in digiKam, choose Settings -> Configure digiKam, switch to the Color Management section, and tick the Enable Color Management check box in the Behavior section. Next, choose the desired color space from the Working Color Space drop-down list. digiKam supports several color space models, including Adobe RGB and sRGB. Which one to choose depends, of course, on your needs (the sRGB vs. Adobe RGB article by Ken Rockwell provides an excellent overview of the two most popular color spaces). The Behavior section also allows you to specify how digiKam should handle photos with profiles that don’t match the working color space, images with no profiles, and raw files with uncalibrated colors.
For example, you can set digiKam to display a color space conversion dialog when the photo you are about to edit uses a different color space than the one you selected in digiKam (see screenshot above).
In the Profiles section, you can specify color profiles for your monitor and peripherals such as camera, scanner, and printer. Obviously, you’d want to select the same color profiles as the working color space. Finally, in the Advanced section, you can enable the Use black point compensation feature which provides a way to adjust black levels of files to match the capabilities of digital devices to manage black.