(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
In printing, proofing is a key process, which is the link between the pre-press process and printing. Its function has two points: one is to check the problems in the production process before printing, so as to find errors in time and make corrections so as not to cause greater losses; the second is to control printing, which gives the printing process a reference approved by the customer For proofs, printing needs to control various conditions and standardize the operation, so that the color and tone of the finished product are not very different from the proofs to meet customer requirements. It can be seen that proofing not only plays the role of checking the upper process, but also controls the lower process.
General proofing mainly includes: screen proofing, laser proofing, traditional offset proofing and digital proofing. Screen proofing is to adjust the color of the screen so that the display effect of the image on the screen is consistent with the color of the printed matter. This kind of proofing is suitable for American editors and advertising designers. The disadvantage of this kind of proofing is that the color display is unstable, and the effect of printing is quite different, and there are too many factors that affect the screen display, which is not easy to control. Laser proofing can adjust the density of each color ink in the printer driver software. Use the output curve correction tool to adjust the ink tone of the primary color (CMYK) ink of the printer to be as close as possible to the actual primary color ink. This kind of proofing has no special requirements for the professional skills of the operator, it is easy to operate, and the data does not need to be converted, but it is far from the color and level of the printed matter. This form of proofing is mostly used in the advertising industry. Traditional offset proofing is the closest proofing method to printing. The materials from the process to the use are basically the same as offset printing. Therefore, the color gamut of the two is the same, and the expression level is also the same. Traditional offset proofing has higher requirements on environmental conditions and process control. Therefore, the operational skills of the staff who are engaged in proofing are also higher. Stability control of proofing color and quality is not easy. This kind of proofing method is more common in printing houses and some companies specializing in proofing work. With the development of printing technology, digital printing and CTP, the printing process is continuously simplified, and digital proofing is also more widely used. It is mainly composed of two parts: color management software and printer. Printers generally use inkjet printers, such as HP 5000, HP 10PS, EPSON 7600, EPSON 10000, etc., and color management software mainly uses ICC characteristic files to do more color correction.
With the continuous improvement of printer ink, paper and color management software, the proofs of digital proofing are getting closer and closer to the effect of printed matter. However, when many printing companies use digital proofs as printed proofs, it is still difficult to follow the proof. Among them, in addition to factors such as poor control of printing conditions in printing plants, irregular printing operations, different proofing density and printing density, etc., some are caused by poor adjustment of printers and color management software.
In order to better use digital proofing, we need to pay attention to the following issues:
1. When choosing a printer, we have to consider the stability of the printer's color, which is why inkjet printers are now used. The color of inkjet printers is stable for a period of time, and no parts will gradually decay. In this regard, it is more suitable for digital proofing than laser printers.
2. The color gamut of digital proofing is wider than the color gamut of printing, so that the printed color can be better expressed.
3. The sample used as the digital proofing simulation is best to be a printed sample, and do not use traditional proofs. Because the condition control and printing principle of traditional offset proofing are different from offset printing, the proofs of traditional offset proofing are different from the printed matter. The digital proof proofs adjusted by this kind of draft will increase the difficulty of chasing the proof.
4. Choose the paper used for digital proofing. Not all printer papers are suitable for digital proofing. When selecting digital proofing paper, you need to consider the color of the paper, the reproduction ability of the tone, and the whiteness of the paper.
5. When adjusting the color of the printer, the relationship between the printer and the paper and ink should be considered. When the paper or ink changes, the printer characteristic curve needs to be readjusted.
6. When the printing conditions, equipment, paper, and ink change, the color and tone of the printed matter will also change. At this time, the printing characteristic curve should also be readjusted.
7. Try to use the same spectrophotometer and characteristic file creation software to complete the production of the printer's characteristic file and printing characteristic file, so as to avoid the deviation of the digital proofing sample due to the slight difference between the different spectrophotometer and the characteristic file production software.
8. In the color management software that can adjust the printer density, it is very important to adjust the printer density before making the printer characteristic curve. The closer the printer density is to the printing density, the smaller the color deviation will be.
9. Ensure that the observation conditions are consistent. The ink characteristics of digital proofing are different from those of printing inks. Although the colors of digital proofs and printed proofs look the same, there is actually a phenomenon of metamerism. When the lighting conditions change, the colors of the two cannot be guaranteed to be the same, and when the spectrophotometer is used to test the color block, the built-in standard light source is used. Therefore, when observing the proofs, there are higher requirements for lighting, and the D65 standard light source is required. Otherwise, there will be different color deviation under different light.
10. Finally, pay attention to control the color difference (â–³ E) between the digital proofing system and the actual printed matter, and control the color difference â–³ E within 5.0. When â–³ E = 2.0, the human eye can hardly feel the color difference; when â–³ E = 3.0, the human eye can just observe the color difference; when â–³ E = 4.0, the two adjacent color blocks are harder to see the difference.
Digital proofing has great advantages in terms of stability and ease of use, but for it to be better used in printing, in addition to asking an experienced person to adjust the printer color at the beginning of the purchase, a special person is required. Maintain the printer and correct the color regularly so that the digital proofing can play its role.
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