How to use spot colors in design plate making
Nowadays, more and more commercial printing materials, packaging and decoration printing materials, especially high-end picture albums, book covers and packaging products, are pursuing the use of special colors to obtain extraordinary effects, such as printing distinctive large areas with spot colors. Background color or thin lines, patterns, etc. Therefore, spot colors are used more and more frequently in plate-making printing. The correct use of spot colors in plate-making printing is very important to achieve customer requirements and the quality of printed products. Based on years of work experience, the author talks about the prepress processing methods of spot colors.
The role and characteristics of spot color
Spot color printing refers to the use of specific color inks, such as fluorescent colors, metallic colors, and bright orange and green, to replace or enrich I and fill the printing of three primary color inks, and each spot color plate requires a special n color separation plate Or channel, making special plate-making film. Spot color printing has the following characteristics.
1. High color reproduction accuracy
Each spot color has its own fixed hue, which can ensure the accuracy of printing color reproduction and solve the problem of inaccurate color reproduction caused by poor ink superposition in offset printing. Moreover, no matter where it is printed, the same spot color can maintain a consistent hue, avoiding color deviation caused by the printing environment, equipment, and process.
2. good field quality
Spot colors generally define colors with solid colors, and can also be used for screening to present arbitrary shades of spot color gradation, such as gold/silver screen overprinting on four-color images to obtain a special effect. In addition, large-area spot color solid printing can achieve solid color uniformity and uniformity, eliminating rose spots caused by multi-color overprinting.
3. Wide color gamut of spot color performance
From the color setting menu of Phtoshop, we can see that any selected spot color is a color that is difficult to reproduce with four colors, and its color gamut is wider than the CMYK color gamut. Therefore, some printing colors with special requirements need to be printed by a professional Color to achieve, and has a certain anti-counterfeiting effect.
4. save costs
The printer is determined by the number of prints. Generally, 1000 folios are printed, and four-color printing is 4 printers. If the designer can design some overprinted color blocks into spot color printing, the printing cost can be reduced.
Spot color design considerations
Some customers require the output center to use the four-color spot-color version of the document for spot-color printing, which makes the output center very difficult; there are also some designers who want to use multi-color printing, but do not know how to make a standard document. I hope the following can provide you with some help, and avoid detours when designing spot color versions.
When determining whether a product is printed in spot color or printed in four colors plus spot color, designers should pay attention to the following issues.
(1) When designing a spot color, you must use the spot color ink option. The ink specified by the software is divided into two categories, namely spot color ink (SpotCoI0rlnk) and four-color ink (ProcessColor. Ink). When designing spot colors, be sure to choose spot color inks (SpotCoIorInk). There is a color version for designing a spot color, and the color cannot be set arbitrarily like four-color printing.
(2) When designing spot colors, the problem of trapping (trapping) should be considered. In order to prevent the spot color from overprinting with the image, it is necessary to hollow out the area corresponding to the image on the spot color. In addition, in order to overprint accurately, the area of the hollow part on the spot color should be slightly smaller than the image area (trapping), otherwise there will be obvious leakage at the edge of the spot color area. Since spot color printing is mostly on-site printing, it needs to be made into a hollowed out spot color when overprinting with the image, and a certain amount of trapping effect is required to achieve an accurate printing effect. If the solid spot color (opaque spot color) is required to completely cover other colors, there is no need to hollow out or trap, but you need to choose the overprint option, and the n spot color ink is superimposed on the underlying image.
There are four principles to follow when doing trapping: all colors expand under black or gold/silver, because black has a hiding effect on other colors; light colors expand under dark colors; yellow expands under cyan, magenta, and black; pure cyan and Pure magenta scales equally below each other.
(3) When making a spot color version with gradation changes, it is necessary to consider the angle of the screen line when the dots are overprinted, otherwise moiré will appear. There should be a difference of 30° between the screen angles of the spot color version and other color versions. If there are 3 spot color versions, it is better to design the screen angles of the 3 spot color versions as 15°, 45°, and 75°. The spot color screen cable is set to 90. , so as not to appear moiré. When printing four-color plus spot color, it is better to make the screen angle of the spot-color version different from other four-color plates by 15°, but the shallower spot color does not need to consider the screen line angle.
1. PageMaker, CoreIDraw, or FreeHand
The spot color setting of these software is relatively simple, as long as the spot color ink (SpotCoIor, nk) is selected in the color setting, but it is better to choose the spot color of the Pantone color library, because it is more popular, the software and Japan have a strong influence on Pantone The support ability of the color library is good, and Pantone spot color inks are also easy to purchase. It is better to manually set the spot color trapping, because the spot color trapping options in this type of software are not easy to grasp (non-professionals try not to use it). Moreover, the results cannot be seen on the screen, and the problems in the settings cannot be seen until the film is released. When manually setting, it is necessary to add a side line to the overprinted solid color block, and set the side line to overprint. At the same time, the selection of trapping value (edge width) is more important, if it is too small, it will not work, if it is too large, there will be obvious boundaries, which will affect the appearance. Generally, the trapping value is determined by the overprint accuracy of the printing machine and paper conditions. For example, when printing with high-quality coated paper and high-precision printing machine, only a trapping value of 0.08-0.10mm is required. Increase, but not more than 0.25mi.
The setting of the cable angle does not need to be considered in the software, you can inform the file that there is a spot color version, and let the output center set it. If it is a large-format file that has been stitched together, registration lines need to be added, but the registration color set by the software must be selected.
2. Photoshop
The production of the spot color version of Photoshop is more complicated, and there are several key points to be mastered.
(1) There are mainly four methods for creating spot color channels.
①Select "New Spot Color Channel" from the drop-down menu of the channel panel, select the color and density in the pop-up dialog box, and then operate on the spot color channel.
②Create a new spot color channel through the selection. Take out or select the image area (generate a selection area), select the "New Spot Color Channel" command in the channel panel menu, and select a color in the pop-up dialog box (same as ①).
③Convert the Alpha channel to a spot color channel. First select the Alpha channel to be converted, then select "Channel Options" from the drop-down menu of the channel panel or double-click the Alpha channel with the left mouse button, and select the spot color channel in the "Channel Options" dialog box; just change the required color and name . Note that the color selection box that pops up at this time is a normal color picker selection box. If you need a Pantone color, click the "Custom" button to switch to the "Custom Color" selection box, and select the desired spot color or custom color. Define colors.
(2) It is better not to use the trapping function in Photoshop, so as not to affect the color of the picture. The author recommends using manual settings for trapping, and you can see the effect after finishing. There are two methods: one is to load the spot color channel selection area on the image in CMYK mode, modify or shrink 1 to 2 pixels under the selection menu, and then fill it with white; After the image part, cancel the selection area and expand the spot color range.
(3) If there is a spot color channel in Photoshop, the format of the stored file is very important. It must be stored in DCS2.0 (*.EPS) format in order to emit the correct spot color in other imposition software. The DCS2.0 format supports multi-channel files, and a CMYK file with an A, ph channel and multiple spot color channels, including low-resolution display images for positioning and high-resolution images for color separation, and Save the rhetoric as follows
In Photoshop, select the PhotoshopDCS2.0 (*.EPS) format and then confirm. At this point, the system defaults to the “Spot Color” option. In the DCS2.0 format dialog box, select "Sweat (8 bits/pixel)" in the "Preview" item, select "Single file with color composite (72 pixels/inch)" from the DCS pop-up menu, and select from " Select ASCII from the Encoding pop-up menu instead of the Include Halftone Screen, Include Transfer Function, and Image Interpolation Method options. Select "Include Vector Data" if the file contains vector data. The specific explanation is as follows.
Preview: Select "8 bits/pixel" to view pictures, and the typesetting positioning is more accurate. The DCS format file is a low-resolution preview file that can display CMYK four-channel files or spot color channel files. But when storing files, be sure to put all the files in one directory for easy scheduling.
Encoding: Different encodings affect file size and processing time, and also affect compatibility. ASCI, "Binary" are commonly used coding methods, and they are all lossless coding. Binary is a higher compression form of ASCII, which is more effective than ASCII, and its file size is smaller than ASC, and its processing speed is faster, but considering ASCII, it has stronger compatibility, so choose ASCII.
Transfer function: The method of controlling the ink concentration by means of a curve is generally selected according to the specific conditions of the printing factory, and it is recommended not to select it.
Vector data: When the layer contains images of vector data such as paths, text, and graphics, it can have better output effects. Saving with this option makes it possible for other programs to use the vector data.
Image interpolation: Check this option to resample the image when outputting, so as to eliminate the occurrence of aliasing.
In addition, when the output center receives the typesetting file made by the above software, it must first figure out how many colors are printed. If it is multi-color printing (with spot color printing), it must pay attention to whether the spot color Correct incorrect documents or return them to customers to make standard documents.
