Color composition
The color structure is a possibility of the image structure in multi-color printing .
Three-color print with color structure
Like color photography, three-color printing works according to the law of subtractive color mixing . All achromatic values in the image arise from the fact that subsets of the colored printing inks CMY mutually neutralize each other and form achromatic values. The printing inks must be coordinated with one another in such a way that roughly equal partial quantities lead to neutral achromatic values. Then they meet the gray conditions .
The first book in three-color printing (a book illustrated using the three-color process) was produced in 1895 by the Förster & Borries printing company in Zwickau .
Four-color printing with color structure (UCR)
In four-color printing, black is generally used to print the fonts. Since it is already present in the process, it is used to reinforce the neutral image depths , i.e. to make them darker and to improve the definition of the image in the dark tertiary colors. In classic four-color printing, a so-called skeleton color separation was produced for the printing color black , which had about 50% to 60% geometric area coverage of the grid in the darkest areas .
Since this classic method can produce up to 360% geometric surface coverage by overprinting the four CMYK color layers at a black image area, the process has gone over to only replacing subsets of the colored printing inks in the dark image depths by replacing the surface coverage of the black printing ink increased accordingly. This method has been under color removal called (Engl. Under Color Removal, UCR), a really nonsensical term that was taken over from the US-American, but has come to be anyway.
Due to the large amount of ink that can be present at each image area due to the overlapping of the four layers of ink, there are enormous problems with the ink acceptance and drying in the high-speed printing machines in conventional four-color printing. And the expensive colored printing ink is wasted in order to create the achromatic values.
Occasionally, instead of the term achromatic structure, one also finds the term black structure .