Color management

Functionality

From step 2 and onwards color management has to be applied. This ensures that the original colors are kept throughout the layout process and that the printed end result is predictable.

Color management crash course

How can we keep the colors consistent all through the digital graphic design workflow? How do we make sure that what we see on the screen is what will come out of the printing press?

The answer is to use a Color Management System (CMS) which in turn uses color profiles (ICC profiles) that describe how color numbers in a document translate to actual color appearances. This means that each input and output device have their own ICC profile (or, in the case of printers, maybe several depending on the type of paper and ink used).

All images exist in a given color space. For example, a camera attaches it's own color profile to the JPEG image it produces (it »tags« the image), so that:

reality = image (ie raw data, color numbers) + ICC profile of  source device

and

(image + ICC-profile of original device) + ICC-profile of monitor  = what you see on the screen (as close as possible to reality)

Color management diagram.

Color management overview

The color space can also be a device independent “working space”, for example sRGB IEC6i966-2.1 or Adobe RGB, which is used when converting between different color spaces.

The CMS handles the color management and also supports on-screen WYSIWYG previewing. Color managed applications can convert images from one device ICC profile to another (a conversion to a different color space).

ICC profiles are based on an open specification and can be used on different operating systems. Note that ICC-profiles for printing should be unique for every printer, paper and ink combination (in practice often only for printer and coated/uncoated paper).

Create a color managed workflow

The following steps are necessary to set up a color managed workflow:

  1. Install and enable a CMS.
  2. Calibrate the screen.
  3. Configure the software.

Software

Create a color managed workflow:

Step 1. Install and enable a CMS

Argyll CMS is a free CMS consisting of a set of command line tools. Ubuntu (12.04) has color management built in (and installs Argyll when needed) and  supports some color calibration hardware out of the box. Ubuntu uses the GNOME Color Manager (which utilizes both the Argyll CMS and colord).

Step 2. Calibrate the screen

The calibration soft- and hardware examines your screen and creates an ICC profile describing how it represents colors. The GNOME Color Manager can be used to calibrate both screens and input devices like scanners.

For screen calibration a colorimeter is also needed, a hardware device which measures the color output of the display. Color Hug is an open hardware colorimeter.

Step 3a. Configure Scribus

1. Setting up color management

In Scribus, chose File > Preferences > Color Management and check Activate Color Management. Specify the following:

  • RGB Images: select the profile used in the creation of images existing in the RGB color space. This is the profile used in the image editor, camera etc. If the images are already tagged with an ICC color profile, that one will be used instead.
  • CMYK Images: select the profile used in the creation of images existing in the CMYK color space. Remember to use the same profile as target profile if you chose to do the CMYK conversion in the image editor program.
  • RGB Solid Colors: the color profile for any RGB solid colors used in Scribus.
  • CMYK Solid Colors: the color profile for any CMYK solid colors defined and used in Scribus.
  • Monitor: select the monitor profile.
  • Printer: Contact the print shop and ask for the printing press ICC profile for the project.
  • To see what the final printing press output will be, check Simulate printer on the screen and Convert all colors to printer space.

Step 3b. Configure GIMP

The photo editing will be done in the RGB color space. There are two things necessary to enable color management in GIMP (2.8).

1. In the Color Management section of the Preferences (Edit > Preferences > Color Management):

  • Set Mode of operation to Color managed display (the default). Set it to Print simulation for soft proofing.
  • Set RGB profile. This is the working profile that GIMP will use with the open images. sRGB or Adobe RGB are good choices.
  • Set CMYK profile used for color conversion. (Not really necessary as we are only going to work in the RGB color space.)
  • Set Monitor profile to the ICC profile for the monitor created in step 2 (“Calibrate the screen”). (Or use the Try to use the system monitor profile.)
  • Set Rendering Intent to Perceptual (best for photographs).
  • Set Print simulation profile to the CMYK (output) profile. This is the profile used during soft proofing (when Mode of operation is set to Print simulation).
  • Set the Softproof rendering intent to Perceptual.
  • Uncheck Mark out of gamut colors. Although it's useful to be aware of colors that cannot be printed GIMP doesn't seem to handle this correctly (Soft Proofing, Gamut warning huge compared to Photoshop).
  • Set File Open Behavior to Ask what to do.

2. In the Color Display Filters dialog box (View > Display Filters), make sure Color Management is active (placed in the right hand list and checked).

For soft proofing enable the Color Proof display filter and tell it to use the Print simulation profile mentioned in above and the Perceptual rendering intent. This filter has been receiving some criticism and it is recommended not to use it and go for the Print simulation Mode of operation instead (Display an image — the Color Management Settings dialog, About CMYK color and Gimp).

Step 3c. Configure Inkscape

Inkscape works in sRGB. SVG doesn't handle CMYK colors. This is not a problem since the color separation will be handled by Scribus. Set up a proper display of colors by chosing File > Inkscape Preferences > Color Management:

  • Display profile: select the monitor profile.
  • Display rendering intent: Perceptual.
  • Simulate output on screen: Checked
  • Mark out of gamut colors: Checked.
  • Device profile: Set this to the CMYK (output) profile.
  • Device rendering intent: Perceptual.
  • Black point compensation: On.

View > Color-managed view should be checked.

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