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  Colour separation Index

How do these control curves work in detail?

The bracketed numbers in the following refer to the preceding illustration.

The Black control curve (4)

This control curve corresponds most closely to the function with which you are familar already. Every theoretical black element value is assigned a raster point size here. This curve can also be used to increase or decrease the black component to darken or lighten the image. But be careful: Too little black can falsify the colours, and too much can cover all other colours. To prevent effects such as the coalescing or breakdown of individual points, you should ease the black control curve at the extremes.

The control curves for Cyan, Yellow and Magenta (5,6 and 7)

These three control curves work in a similar way to the black control curve. Here too, the theoretical colour values will be converted to real, practical colour values. These control curves have a marked effect on the colour balance of the image. For example, a document where the cyan control curve is steeper than the yellow and magenta control curves will appear to have a greenish-blue colour cast. Equally, a document that prints overly red may be corrected with it to make the colours appear natural. It is important to note that the control curve for one colour may affect other colours.

The control curves for UCR (1, 2 and 3)

With these three control curves you determine how much of the theoretical, calculated black value should actually be removed from each printing colour. This makes it possible to correct certain (black) colour errors for particularly light or dark colours. Furthermore, you can use these control curves, in conjunction with the black control curve (4), to determine from which amount of black onwards UCR (undercolour removal) is to take place.

This all sounds very theoretical – and unfortunately, it is! We cannot give a general, practical example for setting the control curves here, due to the many different output devices and printer's colours available. The only way to determine the best values to use is to experiment with the various control curves and print out samples. However, we do have a few tips: If the image is too dark, you should weaken (reduce the slope of) the black control curve, and maybe also the yellow, magenta and cyan control curves. If you make the black control curve too weak, however, the image will have a brownish hue and will lose its colour contrast. You can eliminate colour casts by adjusting an individual control curve or the UCR control curve. For example, if the image is too red, you can raise the cyan control curve. If only the white areas are tending to red, you can lift the lower end of the cyan control curve. However, we cannot give you a set of recipes.There is only one rule: Experiment!

As in the Raster module, you can generate individual colour separation control curves for the entire document, individual pages, or even individual frames. Here too, page settings take precedence over document settings, and individual frame settings takes precedence over both page and document settings.

Calling up the Colour separation module works the same as calling up the Raster generator module. As the Colour separation module does not appear in the Top row, it can be called only with the relevant icon from the Page module or the Print dialog: Go to the Page module; if the Colour separation module is not available, load it by clicking on External modules in the File menu. You may activate the module by double-clicking its name in the module selector box, or by clicking its icon in the Page module or the Print dialog.

The following dialog box will appear:

Under Windows or Mac OS X you can use an ICC separation method. It uses the ICC data from a file named CALAMUS.ICC from the Calamus folder.

Under TOS systems and MagicMac Classic you can only use the well-known Calamus CK7 separation method.

If no frame is selected, the Frame icon will be greyed out and can not be selected. The same applies to the icons for deleting frame control curves and page control curves if the corresponding elements do not contain control curves of their own. Choose an option and click on [OK]. If you have selected an icon to alter a control curve, the slightly modified dialog box will appear whose basic operation was described in the Frame editing module section:

Under the graph there is a field containing the name of the control curve it represents. The number following Layer corresponds to the number in the diagram showing the colour separation process with control curves earlier in this chapter.

You can edit a control curve by using the mouse while holding down the left button. The cursor will appear as a cross hair. Once you have made adjustments, click on [OK] to exit the dialog box, or click on [Cancel] to abort. Note that when you click on Cancel, you will lose changes to all the control curves that you are currently editing, as they will be returned to their original state.

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Last updated on June 24, 2015