Digital proofing technology is one of the popular technologies in the pre-press field in recent years. The so-called digital proofing refers to the page (or printed sheet) data produced by the color desktop system, without any form of simulation, directly output to the color printer (inkjet, laser or other methods) to check the image page of the prepress process Quality, to provide reference samples for the printing process, and to provide users with a basis for signing and printing.

    This kind of digital proofing technology is not simply to find and output color proofs, but through complex color management software, so that the output proofs can reproduce the matching printing proofs, including paper, ink, and printability. similar.

    For a long time, whether the effect of digital proofing is consistent with the simulated printing effect is the main goal pursued by various digital proofing color management systems (CMS). Now the digital proofing system can not only output FM dot structure and continuous tone proofs, but also output the same (dot lines, dot shape, dot angle and dot area) and amplitude modulated dot structure proofs that are exactly the same as the actual subsequent printing. In this way, even if the color separation film has not been output or the printing plate has not been printed, you can see the actual printing effect from the proofs, including whether there are moiré patterns, rose spots, etc., truly what you see is what you get.

    Whether the digital proofing system can be promoted and applied in the pre-press field, in addition to the reproducibility of the characteristics of the printing process such as color, level, definition and even dot increase rate, it mainly depends on the stability, consistency, output speed and output of the system. Many factors such as format size, system investment, cost of consumables, etc. are used to compare digital proofing with traditional proofing.

    After several years of development, the output printer hardware performance of the digital proofing system and the supporting digital proofing color management system and RIP have all been significantly improved. Especially this year, after the digital proofing system breaks through the bottleneck of output speed, this should be the beginning of the real popularization of digital proofing technology in the field of prepress in our country.

    Compared with traditional proofing technology, what are the characteristics and advantages of digital proofing technology?

    1. Color image reproduction performance

    Color image reproduction performance includes image (including line text) tonal range (also known as contrast), solid or saturated color density or chroma, gray balance, and reducibility of gradation curves (including bright, mid-tone, and dark-tone levels) Reproduction and dot enlargement rate reproduction and delicate texture, etc.

    No matter what kind of color management software, by measuring the standard file color block that needs to be simulated for printing and the standard file color block of the equipped printer, the data in ICC format is obtained respectively, and the color management system software calculates the characteristic calibration file required for the proofing process. Profile. In this way, all page image files that need to be proofed (including the data after the RIP of PS and TIFF format files), as long as they are sent to the digital proofing system, the proofing sheets that match the subsequent printing can be output. No matter what kind of paper (such as coated paper, offset paper or newsprint, or even plastic, cardboard and other substrates) and ink series, the digital proofing system can simulate. If there is a slight difference in the quality of the various digital proofing systems at present, this mainly reflects the difference in the performance of the color management software they support.

    Traditional proofing technology, because the proofing machine is different from actual printing in terms of speed, pressure, imprinting method, etc., it is difficult for traditional proofing to simulate actual printing, and it is difficult for printing to catch up with the effect of traditional proofing. In use, printing press operators generally feel that it is easier to simulate, because the color difference between digital proofing and printing in the entire color space is smaller than the color difference between traditional proofing and printing.

 2. Image Resolution

    Since digital proofing systems usually use inkjet printing or laser printing technology, the output is generally frequency modulation dots or continuous tone structure, so as long as the output resolution is above 600dpi, the proofing samples can reach the effect of amplitude modulation dots 150lpi. Most color printers can achieve this image resolution.

    The RIP of the new generation digital proofing system can output amplitude modulation dots consistent with the actual printing effect, so the printer is required to have a higher resolution. At present, the output resolution of EPSON inkjet printers can reach up to 2880dpi, and HP inkjet printers can output up to 2400dpi. There is no problem in outputting AM dot images that are consistent with the actual resolution. Of course, from the point of view of the actual dot structure, the edges of the dots on the proof sheet are not as clear as the actual printed dots, but the subtle differences cannot be seen with the mesh. What people need is that the visual resolution of the entire image is the same as that of printing.

    Traditional proofing may cause the image sharpness to decrease due to inaccurate overprinting, but digital proofing does not have the problem of inaccurate overprinting.

    3. Stability and consistency of sample output

    Undoubtedly, since the digital proofing system is directly sent from the digital page file to the proofing system, before the proofs are output, they are all controlled and transmitted by digital signals. Therefore, whenever the output is output, even if the time is several weeks, months or even years, The output effect of the same electronic file is exactly the same. Of course, the prerequisite for this stability is that the hardware performance of the color printer, such as the ink droplet size, ink, and printing capability, are consistent.

    For traditional offset proofing technology, in addition to paper, ink, PS plate should remain stable (in fact, it is very difficult) and the state of mechanical proofing equipment (such as plate pressure, paper pressure, blanket and pad height, water roller And the pressure of the ink roller, etc.) should be kept normal. The effect of traditional proofing is also affected by environmental conditions (temperature, humidity) and ink management. Due to the influence of many factors such as quantity and uniformity, ink and wash balance, the solid density of the connected proofs cannot be kept consistent during the proofing process, let alone the level of the operator.

    Compared with traditional proofing, digital proofing is hardly affected by the environment, equipment, process, etc., and even less affected by operators. Its stability and consistency are very ideal. Therefore, the digital proofing system is used as a network proofing device, that is, human People can use digital proofing system to output proofs.