Problems related to four colors, spot colors, and light mesh colors

At present, the development and popularization of computer plate making, the control of printing quality in the process of printing and printing has been increasingly transferred to the prepress computer platform for consideration and processing, and designers and plate producers participate in the control of the printing process. Also increasing. For example, in the drafting process, each element must be given a specific attribute, whether it is overprinted, whether it is a simple line or surface symbol, or both the line and the area; whether it chooses trapping or trapping. How to use printing; whether to use four colors, spot colors or their light net colors; how to use them will not cause problems; even care needs to be taken on whether the line, color, font, and size displayed on the computer screen can be used to generate plates. . Because, if printing is used as the final output of map production, these problems must be considered. This imposes higher requirements on our drafting staff. It is not enough to master theoretical knowledge and skillful graphics software operation skills. We should also be clear about the concepts and common sense related to the printing process. On this basis, we will be able to get correct coloring. And color separation, can be used for plate making and printing. The following only discusses printing-related issues in the four-color, spot-color, and light-net colors in the color settings of the graphics software.

The highest dot area rate of surface fill color in CMYK printing

Set the four-color printing manuscript for the area of ​​the highest dot area where the area fills the primary colors, preferably no more than 50%. Because the color space of the colors represented by the computer screen (RGB) and the printing ink (CMYK) is different, the same color is much brighter when displayed on the screen. In addition, the color of different dot ratios in the actual printing, there are still 8% -20% of dot gain and other issues, which in turn makes the actual printed color darker, that is, a higher percentage of color dots. In actual practice, some people set the highest color layer of layered coloring to 80% of the primary color because the screen display is very good, resulting in the mistaken belief that this effect can be printed. However, in practice, it may be printed in the field or approached. The actual color of the field seriously affects the overall effect of the drawing and other elements.

Second, the process of printing four-color (Process) and spot color (Spot) is designed to choose between printing four-color and spot colors, in addition to the local printing conditions, to a certain extent depends on the funding situation, because Adding a single color print adds a printing plate, and a printing unit takes the paper one time to complete the printing of that color. In general, spot color printing is generally used for map printing under three colors. If four or more colors are required, CMYK four-color printing is preferable, while more complex thematic maps and small-scale topographic maps often require four-color printing. Spot colors (for example, six colors, seven colors, or eight colors, etc.). Because four-color printing can combine most of the arbitrary colors, and some special color expressions also require the addition of spot colors, because the spot color is a pre-mixed ink, it has four colors incomparable expression color accuracy features . In addition, there are two things to note when using color settings with graphics software:

1. If you convert the cyan color to the primary color (CMYK four colors) before the output, do not assign the spot color to the default color separation. This will cause each spot color to have a color separation in each country. The film, thus resulting in the error of four times the number of color films issued spot color film. The correct approach should be to select the "spot color conversion to the primary color" option, and then proceed to publish;

2. It should be clear that the color gamut in the spot color library is wider than the color gamut printed with the CMYK four-color printer. Therefore, in the process of converting the spot color to the primary color, some spot colors cannot be completely faithful, but some color information will be lost. ;

3. When using spot colors, note that different software may have different names for the exact same two colors. For example, PANTONE 185 is named PANTONE 185 CVC or PANTONE 185 CVV in FreeHand, and named PANIONE 185CV in PageMaker. So when the FreeHand graphic object is put into PageMaker, there are three names for the same color, which will result in a different color name of a spot color output into a different color version of the error. It is best to use a custom method to set the spot color, and make all the color names unified to the grouping software used for publishing, to avoid output errors.

Third, the concept of shallow network color (Tint) and its printability shallow network refers to a base color plus Internet mesh generated by the screen color, it exists a certain percentage of the base color, specifically used in the software note:

1. Avoid the use of shallow light nets and very slight shallow web changes. Because 2% or less of the light color of the base color can be expressed on the film, it is difficult to print. At the same time, it is almost impossible for a printing machine to duplicate the difference of dot area percentage of 1% (even if it can be distinguished on the screen), which is why the amount of increment in the shallow network setting menu of the graphics software is 5%.

2. Avoid using light mesh colors on thin lines. Because the thin line added to the shallow mesh has a floating feeling, the display and printing are very much like dirty spots and misprints, which greatly affect the effect of the drawing;

3. Shallow webs are cumulative. If 60% shallow webs are used for graphics that are already 50% lighter, the shallow webs of this base color will be subtracted twice and become 30% of the base color, twice. Superposition is a multiplication relationship;

4. Carefully use or avoid the use of shallow mesh settings for the primary colors (CMYK). Since each spot color has a fixed hue, if a certain percentage of light mesh color is used, the hue of the color will not change, and only the saturation will change, which can ensure the accurate color transfer. Features, one of the main advantages of spot colors. The primary colors are not so simple. The primary color mixture is the color defined by the four primary colors of cyan, magenta, yellow and black in different ratios and thus defined.

For a certain primary color mixture, its four-color percentage is specific. If a shallow mesh is used for the color, all percentages of the four colors contained will be equally scaled, and a certain percentage of the primary colors will have a light mesh color. The hue is the same, but the hue of the different light network colors composed of the four primary colors is not uniform. This is because the different saturation of the primary color mixture shows the four-color percentage ratio, which is not an equal-scaling relationship, but varies according to the proportion of the neutral gray balance of the ink mixture. So if you add a mesh to the primary color, the hue of the color will inevitably shift. This is especially noticeable in more precise printing.

Reprinted from: Chenyi Printing Network