Tips & Tricks: Color Sets in Image Control and Axis Control

When do you create new color sets and how?

Color reproduction on the press sheet is influenced by the properties of the inks and the color of the paper. To ensure that the various inks are applied consistently onto different papers, it is necessary to correct any deviations. This can be done by defining new target values and saving them as colorimetric Lab values and densities together with the paper white in a "color set". The Lab values depict the inks in a color space, while the color density quantifies the ref lective response of the ink.

The Prinect Image Control and Axis Control color measuring systems come supplied with the "Heidelberg" and "Standard" color sets. These sets are based on the inks and papers that Heidelberg uses when test-printing a press in the factory. They therefore already contain target values for the required coloring and the Lab values of the paper, from which the target coloring was taken. Prepared configurations for each grade of paper (smooth, matte, natural) are also available and need to be taken into account in the printing process. A new color set has to be created for each ink and grade of paper used. Likewise, a new color set is required when target values change - for example, for different densities in printing. The remission spectrum (which exactly defines how a color looks) must also be calculated by measuring the target value of the ink actually used. However, because the paper's coloring significantly impacts the remission spectrum of the ink, it is also important to know the color of the paper from which the target value was taken. This must therefore be measured and also saved in the color set.

Here is how it is done:

  with the color or target values
      used.
7.   Insert the Lab value for the
      paper white from the current
      press sheet into the new co-
      lor set.
8.   Now you can add the process
      and special colors to the color
      set from the current sheet (or a
      sample). If you wish to use gray-
      patch control, the corresponding
      gray patch - formed from 70 per-
      cent cyan, 60 percent magenta
      and 60 percent yellow - must be taken from the current sheet/sample.
9.   Exit the menu. The new values are saved automatically.