At present, the development and popularization of computer cartography, the control of the quality of map printing in the process of printing and printing has been increasingly transferred to the prepress computer platform for consideration and processing. Map designers and mappers participate in maps. The proportion of control in the printing process is also increasing. For example, during the mapping process, it is necessary to give clear attributes to each map element, whether to select overprinting, whether it is a simple linear or planar symbol, or whether it is in both line and area; whether it is trapping or trapping. How is the method; printing is the use of four colors, spot colors or their shallow mesh color, how to use will not cause problems; even need to care about the line screen, color and font size displayed on the computer screen and its size can be printed Version. Because, if printing is used as the final output of map production, these problems must be considered. This puts forward higher requirements for our cartographers. It is not enough to master map editing knowledge and skillful graphics software operation skills. It should also be clear about the concepts and common sense associated with the printing process, on which basis it can be correct. Color printing and color separation, can be used for plate making and printing. The following only discusses the problems related to printing in the four-color, spot-color, and light-net colors in the color setting of the graphic software.
The area ratio of the highest dot area of ​​the fill color of the area in the first and the fourth color (CMYK) print map. In the four-color printed map, the area ratio of the highest dot used to fill the primary colors in the area is preferably not 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 site seriously affects the overall effect of the map and the representation of other map elements.
Second, the process of printing four-color (Process) and spot color (Spot) map design to print between the four-color and spot colors to make a choice, in addition to local printing conditions, to some extent depends on the funding situation, because For each additional color print, one printing plate is added, and one printing unit feeds the paper one time to complete the printing of the 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 preferred, 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 points 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, please do not assign the spot color to the default color separation. This will cause each spot color to have the four-color color separation film of each country. As a result, errors of four times the number of color separations of the spot color film are caused. 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, pay attention to the different software. For the same two colors, their names may be different. For example, PANTONE 185 is named PANTONE 185CVC or PANTONE 185 CVV in FreeHand, and is 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 as a percentage of the basic 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 printer to duplicate the difference in dot area percentages (even if it can be distinguished on the screen), which is why the incremental amount in the shallow 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. Care should be taken to avoid or avoid the use of shallow mesh settings for 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 transmission. 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 proportions 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.