Spot color printing precautions

First, spot colors and their characteristics

Spot color ink is a kind of pre-mixed specific color ink, such as fluorescent yellow, pearl blue, metal gold silver ink, etc. It is not mixed by CMYK four colors, and trapping means accurate color. The printing excellence network analysis has the following four characteristics:

1. Accuracy. Each color registration has its own fixed hue, so it can guarantee the accuracy of the color in printing, thus solving the problem of color transfer accuracy to a great extent;

2. Field performance. Spot colors generally define colors in solid colors, regardless of how light they are. Of course, spot colors can also be screened to present any shades of spot color;

3. Opaqueness. Spot color ink is a covering ink, it is opaque and can be covered in the field;

4. Wide color gamut. The color gamut in the color bank is very wide, exceeding the RGB performance gamut, not to mention the CMYK color space, so a large part of the color is not present with the CMYK four-color printing ink.

Second, the reason for choosing to use color in color dot printing

In color dot printing, the characteristics of spot inks are often used to select and use them. In general, printing is generally used in two situations:

1. In order to print on the printed matter, the color of visible light outside the color gamut of some CMYK four-color printing inks can be printed. The color gamut of CMYK four-color printing ink is obviously insufficient compared with the visible color gamut, while the color gamut of spot color ink is wider than that of CMYK four-color printing ink, so it can express many colors other than CMYK four-color ink;

2. To compensate for the lack of printing technology. Due to the errors of various processes in the overall printing process, equipment maintenance, operating environment, artificial omissions, and mechanical wear and tear, it is difficult to obtain even and smooth dot colors when printed at 153 or less dots. At this time, we can use the same color. The full version of the color (ie spot color in the field) instead of a small dot for printing, it can be easier to get a flat large area color. In addition, in order to be able to clearly represent the finer graphs, such as mixed strokes or incontrasting lines with finer strokes, the printing industry often uses spot color processing to ensure that the fine line strokes are sufficiently realistic and delicate.

Third, pre-press use of spot colors should pay attention to some issues

1. The unity of spot color names.

2. Spot color screening angle. In general, spot colors are printed in the field, and they are rarely processed at the outlets. Therefore, the point of spot color screening is rarely mentioned. However, when using a lighter mesh color, there will be problems with the design and modification of the spot color screen dot. If there is an overprint area between the spot colors of the outlets and the colors printed by other outlets, the issue of spot color screening must be considered.

3. The conversion of spot colors to printing four colors. Designers of printing companies often use the colors in the spot color library to define colors and perform coloring when they are doing graphic design. In color separation, they are converted into CMYK printing four colors. Pay attention to three points: First, the color gamut of the spot color is larger than the color gamut of the printing. In the conversion process, some spot colors cannot be faithfully completed, and some color information will be lost. Second, the spot color conversion must be selected in the output. Become a four-color "choice, otherwise it will lead to an output error; Third, do not think that the CMYK color numerical ratio displayed next to the spot color number allows you to reproduce the spot color with the same four-color ink of the same CMYK composition.

4. Spot color trapping. Because the spot color is different from the printing four colors, it usually does not generate a color with the overprint of two spot colors. Intuitively, it will get a very dirty color effect. Therefore, if a spot color is defined, the printing generally does not use overprinting ( Overprint) instead uses Keepaway. In this way, when using spot colors, as long as there are other colors beside the spot color pattern, proper trapping should be considered to prevent the problem of dew-white spots.

5. Spot color matching system. When choosing a computer color matching system, first of all, it should be clear which are the spot color systems and which are the CMYK four-color printing systems, so as to know whether the color you choose to use in the system will have color conversion and whether it will Color distortion occurs.

6. The cost of spot color printing. General spot color printing is generally used for printing below three colors. If four or more colors are required for printing, printing companies generally use CMYK four-color printing. Because CMYK four-color printing is basically based on dot overprinting, and using spot colors is basically printed in the field. Although the spot color is usually only used locally in the image, it is customarily used twice the price of ordinary printing ink. To estimate; In addition, if the same layout has four printing colors, it is equal to one color for printing. If the printing machine has no extra printing units, it will take twice as much time to print. It's even higher.