The application of digital proofing involves not only the plate making shop, the printing shop, but also the advertisers. It can provide advertisers with the same copy in the advertising department of the newspaper and establish a bridge with customers. Secondly, digital proofing can fully inspect and control the processes from platemaking to printing, and promote the overall improvement of newspaper printing quality.
The following uses proofing software as an example to introduce the application of digital proofing, which uses the RIP proofing method. The proofer is the HP Designjet 4000.
Before the formal proofing, some test plates need to be printed, the colorimeter is used for measurement, the color management calibration is performed on the equipment, and the equipment characteristic curve of the printing machine is generated (ICC Profiles document). The proofing machine's equipment characteristic curve is relatively good, but it is more complicated for the printing press. The printers in the printing center of the author have a large number of presses. There are six large newspaper rotary presses, and the brand is different. The working principle is different. There are both mechanical transmission and shaftless transmission, and even the same printing press, different printing Between the color groups, due to the respective characteristics of the drum, the blanket, etc., the characteristics between the different printing machines, between the different printing color groups, and between the different cylinders, their characteristics may not be exactly the same. From the point of view of color management, theoretically, the device characteristic curve should be made for each printing press and even for each printing color group. For commercial printing, this should indeed be the case. However, newspaper printing is not as accurate as commercial printing in terms of quality. Moreover, for such a large number of devices, if they are individually performed one by one, not only is there a great deal of complexity in the generation of profile files in the early stages, but in actual production, different proofs must be proofed for different printing devices. This is time-consuming and laborious, and it is not advisable for newspapers that are time-sensitive. Therefore, during the actual testing, we selected a printing machine with a good working condition, stable production, and high printing quality to make the equipment characteristic curve. For other machines, we used the printing product of this printing press to color. This will not only ensure the consistency of the proofing effect and the actual printing effect, but also ensure that the newspapers printed by multiple machines are basically the same in color and save the time for proofing. This fully meets the characteristics and requirements of newspaper printing.
After getting the sample, don't rush to measure it. Let it dry naturally for some time, because the moisture on the surface of the newspaper is not completely absorbed; it can't be measured after one day, and the result is not accurate. Then use a spectrophotometer to measure the L*a*b* value of the IT8 color scale. It is best to use a spectrophotometer dedicated to color management when measuring. Since the IT8 color scale has 840 color patches, it is time-consuming if it is measured one by one using an ordinary spectrophotometer. The dedicated spectrophotometer can be quickly completed in just a few scans. The test results are then passed directly to the color management software for analysis and the printer profile file is generated.
The same is true of proofers. The proofer is adjusted to the optimum state and the basic calibration is performed by the program of the proofer to bring it to an ideal color gamut range. Then print the IT8 color mark, and create the profile file of the proofer as above. Then configure it in the digital proofing software, but the work is not completely over. Because the HP Designjet 4000 is a four-color print, its color gamut is smaller than the printer's color rendering range. Therefore, in actual production, we must make further adjustments based on actual results. Most midtones have no problem, mainly because there are some color differences in some saturated shades. If each newspaper's head is generally M100%, Y100%, it is difficult to accurately restore the print sample, so these saturated colors need manual adjustment. In addition, the production of ICC Profiles should be updated regularly. For a newspaper printing factory, although there is no commercial printing that requires precision, it must be produced once every six months to a year.