Spot
color is different from the color of CMYK. It refers to a color not synthesized
by printing CMYK, but printed with a specific ink pre mixed by the printing
factory or produced by the ink factory. For each spot color of printed
matter, there is a special color plate corresponding to it during printing.
Use
spot color can make the color more accurate. Although the book printing color cannot be
accurately represented on the computer, the accurate color of the color on the
paper can be seen through the preprint color sample card of the standard color
matching system.
Ink
printing color, there are generally two methods
(1)
Printing color using four-color ink
The
mixed printing ink modulates the spot color, that is, spot color printing is
used, and the color is expressed by solid color or dot. The color assignment
and plate making methods of the two methods are different in printing design.
Spot
color printing process is often used to print large area background color in
packaging printing. The covers of packaged products or books and periodicals
are often composed of uniform color blocks of different colors or regular
gradual color blocks and characters. These color blocks and characters can be
separated and overprinted with four primary colors of ink, or spot color ink
can be prepared, and then only one kind of special color ink can be printed at
the same color block.
Under
the condition of comprehensively considering improving book printing quality and saving
overprint times, spot color printing is sometimes selected. The ink prepared by
spot color printing obtains the color according to the mixing principle of
pigment subtraction method. Its color lightness is low and its saturation is
high. Compared with four-color printing, it is easier to obtain the printing
effect of uniform and thick ink.
For
the color block printed by four-color printing process, because most of the
colors constituting the color block are composed of a certain proportion of
dots, when printing dots, the change of ink layer thickness and the change of
printing process conditions can cause the change of color intensity and dot
expansion, resulting in the change of color. Therefore, the color block
overprinted by four-color printing process is not easy to achieve the effect of
uniform ink color.
The
cost of spot color should be considered from the perspective of economic
benefits, mainly to see whether the spot color printing process can save the
number of overprint. Because reducing the number of overprint can not only save
the printing cost, but also save the cost of prepress production. General spot
color printing is usually used for printing below three colors. If more than
four colors are required, CMYK four-color printing is appropriate in terms of
cost.
In
addition, if there are already four printing colors in the same layout, it is
equal to one more color for printing. If the printer does not have redundant
printing units (such as less than four-color printer or four-color printer), it
will take twice the time to finish the book
printing, and the cost will be higher.
If
there is both a color hierarchical picture and a large-area background color in
one picture, the color hierarchical picture part can be printed in four colors,
and the large-area background color can be printed in spot color. In this way,
we paid a slightly higher cost, but obtained high-quality products. Because the
four-color printing part can correctly restore the picture by controlling the
field density, and the bottom color part can obtain the visual effect of
uniform and thick ink color by appropriately increasing the amount of ink.