Printing spot color features and operation (below)

3. Spot color to print four-color conversion. Many designers often use the colors in the spot color library to define colors and perform coloring when they do graphic design. In color separation, they are converted into CMYK printing four colors. At this time, 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 output must be selected. Spot color conversion becomes a four-color selection, otherwise it will result in an output error. Third, do not assume that the CMYK color numerical value 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 ( If you can use it, you will not need to use spot colors. In fact, if you do so, the resulting color will have a large gap in hue.
4. Spot color trapping. Because the spot color is different from the four-color printing (printing four-color inks to generate inter-color printing on each other, that is, the ink has transparency), it is not usually used to generate a color between two spot colors, which is intuitively speaking. Get a very dirty color effect (of course there are exceptions, such as the intention in the design of the use of spot color overprint processing to produce the required, superimposed blend of the third color, this third color is full, thick and real, such as: spot color yellow On-press embossed spot color red, two colors superimposed to produce a steady dark red, often used as a book cover, etc.), so the definition of spot colors, generally do not use overprint (Overprint) but to use empty ( Keepaway). In this way, when spot colors are used, as long as there are other colors next to spot color patterns, appropriate trapping should be considered to prevent the problem of dew-white spots. (The method for trapping spot colors and related technical issues are more complex. This is not repeated).
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. For example, color matching systems commonly used in graphic software include PANTONE, TRUMATCH, FOCOLTONE, TOYO ColorFinder, ANPA-COLOR, RIC Color Guide, etc., of which TRUMATCH, FOCOL TONE, and ANPA COLORR are based on a four-color printing system. Others All belong to the system of spot colors (the PANTONE system covers a wide range of colors, both process and spot colors). This means that in spot color matching systems such as PANTONE spot colors, TOYOColor Finder, and RIC Color Guide, many of these colors have exceeded the four-color color gamut and cannot be reproduced with four-color inks. The system provides CMYK combined values. It is only an approximation. So if you have selected the colors in the spot color matching system and printed them in four-color printing, or referenced the corresponding CMYK values ​​that the spot colors displayed in the system, and used these values ​​to replace the four-color printing. The original spot color, the result will definitely lead to color distortion; Second, it should be understood that the spot color matching system when doing color separation processing, unless specifically set to convert the spot color to CMYK four colors, otherwise, each used Spot colors are automatically divided into a single color version. In the same way, after printing the colors in the four-color color matching system for coloring, the color output will automatically follow the color's own CMYK ratio to the four plates without generating more. The color version. Second, note that in the context of a dot-matrix diagram, the selected color (for example, a spot color) is automatically converted to the same color mode as the data file to which the color is applied (for example, CMYK four-color mode) after it is used on the canvas. .
So in the dot matrix drawing software, for the spot color, it must be deliberately added or specified (for example, adding and defining a spot color in Photoshop, there can be two cases: if the spot color is applied as a hue to the entire image , you need to convert the image to a two-tone mode and apply a spot color on one of the two-tone plates; if you use a spot color for a specific area of ​​the image, you must create a spot color channel; and in a vector drawing environment, When a spot color is selected or defined, the color will always exist as a spot color attribute unless the spot color attribute is specifically changed or converted to a process color (eg, a spot color added and defined in Yiiustrator, even if it is referenced In other Illustrator data files, data files that will use this spot color are opened with other vector software, and the color attributes of this spot color are not changed.)
6. Spot color printing costs. Generally, spot color printing is generally used for printing below three colors. If four or more colors are required for printing, four-color printing of CMYK is suitable. 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 more color for printing, if the printing press has no extra printing units (such as less than four color printing machines or four color printing machines. ), it will take twice as much time to print, and the cost will be higher.