The Total Ink Limit (TIL) is also located under File>Color Settings>CMYK Setup and is another important parameter to consider. . Improper handling may result in moire. You must try to control the total amount of ink between 340-380%. That is, if you can't pull down the Lc and Lm curves, you will increase the amount of ink by 200% in the dark tone area, resulting in a 500% unimaginable amount of ink in the screen separation. By specifying a lower total amount of ink, not only can the color reproduction ability be improved, but also the amount of ink can be reduced and the cost can be saved. Dot enlargement Prevents dot gaining Additional channels must be manually adjusted (in the CMYK Setup window) and each channel is individually adjusted. The reasons for this adjustment are twofold. First, the color value of the light color ink is greatly reduced, and the effect of dot gain on the high tone and 25% tone area is not significant. Second, the probability of dot gain occurring in this part of the image is very small. When printing, you must carefully observe the difference between the printed image and the original image. If further corrections are required, you can brighten or darken (reduce or increase the printing density of the ink), or return to the processing stage and adjust each time. The color values ​​of the color channels make them brighter or darker. Experience is the best guide, so the first few images in six-color printing have the most experience. For users who are printing six colors for the first time, it is best to record each change carefully. The benefit of using a two-tone process for printing lines is that the number of halftone screen lines can be reduced without significant loss of resolution. This facilitates the work of the two methods. First, if the number of screen lines is reduced (using larger dots), dot gain and tone reproduction are controlled, and virtual halo is also easy to control. Moire is also not obvious. This makes the entire image easier to control and better consistent. On the other hand, if the number of screen lines remains at the usual level, the appearance with increased resolution will be seen. The details will be rich, and the visual half-tone rose pattern will be reduced. This is very important for POP. Because the halftone pattern in the POP can reduce the quality of the image. The adjustment of the number of lines is the same as the halftone screen adjustment discussed in the next paragraph, which is modified in the "Page Setup" window (File>Page Setup>Screen). Separation of screen angle For the six-color printing mode, the control of the screen angle is relatively easy. When the cyan and magenta channels are separated, they effectively become dual-color channels. This means that when the Lc halftone dot is mixed with standard cyan ink, the minimum angle between every two colors must be kept at 30°. Typically, the cyan and magenta halftone screen angles differ by 60° (eg, 15° and 75° or similar values). With this in mind, make a simple transition to the web corner. Lc is printed at a 15° screen angle and standard Cyan is printed at 75°. Lm is printed at 75° and standard magenta is printed at 15°. Now look at the 60° difference between Lc and Lm, and the difference between standard cyan and magenta is 60°. Both conditions can be satisfied, and any color will not conflict with other colors. Also remember to rotate all the corners away from the 0°, 45°, and 90° corners of the traditional lithographic screen. These angle conflicts can create serious moiré patterns. One of the most common rotation angles is to increase 7.5° to avoid the corners that cause conflicts. For example, if the lithographic screen angles are 0°, 15°, 45°, and 75°, the rotated screen angles are set to 7.5°, 22.5°, 52.5°, and 82.5°. Proofing is a weak link for multi-channel color separations. No analog proofing system (Matchprint, Waterproof, etc.) gives a better preview. Several digital proofing programs will enter the market, but now the only reliable proofing method is proof printing, which is expensive and time-consuming. Using DCS 2.0 to store, place, and output color channels in the six-color channel is best used in the DCS 2.0 file format. This is a special version of the DCS format developed by Quark a few years ago. It uses a low-resolution placement icon and automatically replaces it with a high-resolution image on output. DCS 2.0 is used in Photoshop. The separation file must be converted to multi-channel mode (Image>Mode). The Lc and Lm channels must be named and set as spot channels. The number of lines and net angles for each channel must be set as described earlier. If the output is through a company with screen printing image separation experience, the last step may not be performed. However, if you do not know how to output the file, you must complete the final step. To save the file, select File>Save As Photoshop DCS 2.0, then select a single file and check the "Color Composite" option. These options can be output directly from Photoshop to the imagesetter, or output to the imagesetter via layout software such as QuarkXPress, PageMaker, etc., or output to the imagesetter via drawing software such as Illustrator, Freehand, CorelDRAW, etc. In either of the above cases, when the image is placed in drawing software or layout software, all of the color separations are entered into the software as one piece of the image. You can now use Lc and Lm as types, boundaries, or backgrounds. If you do not use the DCS 2.0 option, you can select the Split Channel command in the channel's floating panel. It is now possible to output or place each channel separately. This method takes a little time to understand, but it is a versatile method for handling multi-channel images. Printing Production In general, six-color images can be printed from the darkest to the brightest colors. It has been said before that this method of black printing can reduce the negative effect of black. In fact, when black prints first, other overprint colors will also suppress black. This allows the darkest color to be revealed without being completely buried in black. My specific printing sequence is black, cyan, magenta, yellow, Lc, and Lm. Color ordering is useful because it allows four colors to be printed first along the conventional process. The real difference is in the last two colors, and these are the brightest colors, so the main color is less likely to make mistakes. Key points can be placed in key areas to ensure that the last two printed colors are printed correctly. If a densitometer is used to measure the color of a controlled print, the six-color process is consistent with the traditional four-color process. By measuring the solid color patches of light-colored overprint inks, the density of high-profile, mid-tone, and dark tone is displayed. When the job is completed, the color matching, gray balance, and overall visual effects are strictly evaluated. The initial experiment of six-color printing is the same as the traditional four-color overprinting, but it is not too strict. Mesh Count and Tension Because only shallower values ​​are printed in existing overprint inks, mesh selection and tension remain consistent with traditional prints. According to the conventional production requirements, the difference in the tension of each color screen is kept within ±1 N/cm. High tension can be better controlled, so it is necessary to try to keep all the screen tension at a minimum of about 25 N/cm. If you have problems with the consistency of the screen tension or moiré due to tension changes, six-color printing will help you solve these problems. The successful six-color printing of six-color printing is not the destruction of traditional printing, but the expansion and progress of traditional printing. The goal as a printer is to make profits greater than inputs. Two additional colors are added, but the profit from printing control, the enlargement of the tonal range, the reduction of moiré, and the enhancement of color expression capabilities are far greater than the cost. This special color model is one of many different color separation technologies and it is classified as a field in which digital color science continues to develop. The 150-year-old traditional CMYK model is giving way to multi-spectral multi-channel color separation technology, and will see and hear more about it in the future. *************Figure 5: Completion of six-color printing************* When yellow and black are printed, dark green and dark magenta are printed again, and then Printed light blue and light magenta, the tonal range has been significantly expanded, with good high-profile and dark-sounding details and a pure ash for the entire hue area.