Creating print artwork with Inkscape and Scribus

Generics

Print firms that don't use a standard profile, such as sRGB or CMYK, usually have their own profile that they can send you. If in doubt, ask for the color profile from the firm. Less pricy printers often save themselves this effort and work without any color management.

Such was the case in producing the sample CD cover (Figure 3). It shows a distinct, yet tolerable deviation between the screen display and print. I used the device profile common in Europe known as ISO Coated v2 . Tailored to common offset printing machines, it comes close enough in color reproduction, even when the printer works without color management.

Figure 3: On the left, you can see the final product; on the right, you see the view in Scribus. Although the differences are relatively small, they're nonetheless perceivable.

When selecting generic profiles use Coated for coated paper and Uncoated for uncoated paper (colors appear less bright). In any case, use generic profiles for monitors and printers without color management preference, because at least the conversion from RGB to CMYK color space gets done (see the "RGB and CMYK" box).

RGB and CMYK

The human eye has three types of color receptors that react to different wavelengths of light. You can, therefore, achieve any desired color effect by mixing red, green, and blue light.

Although bright pixels add more light to the screen (additive color mixing), color printing does just the opposite: The print colors filter out spectrum elements of the reflected white light of the paper, composed of equal parts of red, green, and blue (subtractive color mixing).

This technique uses other primary colors. If the screen has red and green pixels together, they appear yellow to the eye. If you mix red and green watercolors, you theoretically get black; however, because of the imperfect filtering properties of the pigments, it's more like gray. The red watercolor lets red light pass and filters out green and blue, whereas the green watercolor lets green light pass and blocks the red and blue. This combination thus absorbs all three color components. That's why the color printing needs primary colors that filter out not two, but just one component perceived by the eye as red, green, and blue.

This is the case on screen with a mix of two RGB components, as Figure 4 shows: cyan (green and blue), magenta (red and blue), and yellow (red and green). The additional black is the contrasting color used for text.

Mathematically, the conversion from RGB to CMYK seems simple, but in reality you need to take into account the imperfections of color pigments. On screen, a red illuminated point emits small amounts of green and blue that brighten the color. Printer pigments, on the other hand, absorb spectral components that they should actually allow through to a lesser degree. The slight yellow paper color attenuates blue shading somewhat.

Figure 4: Subtractive color mixing in which the color pigments filter out spectral components from the white paper requires other primary colors (cyan, magenta, and yellow) as the additive color mixing of the red, green, and blue pixels of the monitor.

Profiling

To provide a color profile for the document, open File | Document Properties | Color Management and link the desired profile with the document. So far, Inkscape simulates the print colors in the CMYK color space only on screen. Even if you use the CMYK tab in the color picker, the program internally calculates the RGB colors. To change this, left-click an object with color fill and open the context menu Fill and Stroke . Change to the CMS tab and choose the color profile already selected for the simulation of the printing colors (Figure 5).

Figure 5: On the CMS tab of the Fill and Stroke dialog, you can link the colors of the object with the profile used for the printer property.

Inkscape doesn't create consistent CMYK documents, but instead assigns individual colors to the CMYK color space. These arrive as such in Scribus when importing the SVG files created in Inkscape. This color management and SVG import into Scribus create an unbroken workflow between the two programs, even with continuous color management – at least in theory. In practice, however, the shortcomings of the Scribus import filter make it far from perfect.

Thus, all graphic effects are lost during the SVG import. Even the simple blur of the green color wedge disappears, along with the drop glow in the text. To package these effects with help from Scribus into a standardized CMYK PDF, the only way is through a bitmap export from Inkscape. To make matters worse, the drawing program exports bitmaps and PDFs exclusively in RGB color space, which is why it's not suited for generating true color print templates.

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