About Digital Proofing Reviews

At present, people are most concerned about digital proofing, there are two points, first, digital proofing can replace the traditional proofing it? Second, what kind of performance index is a good digital proofing system? To answer these two questions involves the evaluation of digital proofing.

For the comparison between digital proofing and traditional proofing, there are many materials and articles introduced. In short, the reproducibility of proofing images refers to the proofs (including digital proofs and traditional proofs) of proofs in terms of tone range, neutral gray balance, level reproduction, color reproduction, and clarity, as well as simulations. The consistency (or similarity) of printed proofs. There are also sample proofs, proofing speeds, proofing costs, and other performance aspects. The key to evaluation is digital proofing and traditional proofing. Which process (technique) can better simulate printed sheets. The evaluation includes two aspects of objective measurement and subjective evaluation. Here, more emphasis is placed on the use of instruments to measure the consistency between proofs and printed sheets.

We know that to ensure the reliability of the measurement results, we must first ensure the stability of the printing proofs, that is, the printed sheets providing test and comparison must be the raw materials, equipment conditions, printability, and even environmental conditions involved in the printing process. Under stable conditions, the printed sheets can be used as the basis for assessment.

For traditional proofing, the ink may not be the same for traditional proofing and normal printing. Even if the raw materials are the same, the speed, pressure, printability, and even the printing plate of the proofer are inconsistent with the printing, so it is difficult to ensure The consistency of the two, not to mention the adjustment of the proofing machine, the operation process varies from person to person, and the process of proofing one by one at a time is very unstable (such as ink volume, water balance, etc.), it is difficult to achieve the absolute between a batch of proofs Consistent.

Regardless of whether it is for traditional proofing or digital proofing, the main test method is to use a colorimeter to test the chroma and color difference between proofs and printed sheets. Usually use the 928 color block data provided by the ISO 12640 "standard color image data" international standard. Firstly, the color separation sheets containing these 928 color patches are output according to the normal process. After printing, printing is performed under stable printing conditions, and the obtained printed sheets are used as the basis for reference, and then the conventional color proofs are used (ie, the same color separation is used). Tablets, proofed by printing, and directly using the digital proofing system to obtain two kinds of proofs, respectively, with the printed sheet for comparison measurements. Of course, the digital proofing system has been calibrated according to the normal color calibration procedure through printed sheets. Using a colorimeter to measure the color difference between the two proofs and printed sheets, corresponding to 928 color blocks.

Through a series of tests conducted in the near future, it was found that proofs of digital proofing were within the range of the color space that the entire ink and paper can reproduce, regardless of the adjustment range, neutral gray balance, and level reproduction (mainly simulated effect of printing dots, and Brightness level reproduction, etc., or color reproduction, etc., are better than traditional proofing, that is, the average color difference of digital proofing is smaller than traditional proofing. Needless to say, the repeatability and consistency of digital proofing cannot be compared with traditional proofing. In the case of the use of coated paper, some digital proofing systems can do more than 95% of the color blocks after the automatic calibration, and the color difference (â–³E) value is less than 5; under newsprint conditions, more than 90% of the color blocks, The color difference is less than 8. If supplemented by manual fine-tuning, the color difference can be further reduced. This means that the current results of digital proofing are already very similar to printed ones. Although the current network structure of digital proofing is still not an AM network (there will be a prototype RIP of the AM network structure in the near future), mainly FM network or continuous tone, but no difference can be observed with the naked eye. Undoubtedly, whether visually judged or measured by a colorimeter, digital proofing can completely replace the traditional proofing process in image reproduction. It can not only check the quality of the plate for the preceding process, but also provide reference proofs for printing (especially stable Reference sample).

In addition to the image reproduction and consistency that people are most concerned about, in terms of output format and proofing speed, digital proofing can produce a 720×1020mm proof within a few minutes, truly “stand ready”. As for the cost of proofing, it cannot simply be compared with the current wages, although the number of digital proofs (three sheets) is already lower than the cost of a set of traditional proofs. The cost of traditional proofing not only includes the cost of paper, ink, and PS plates, but also includes the depreciation of the proofer, the use of the plant (rent), environmental control costs (air conditioning, heating, humidification, etc.), utilities, and labor costs. At present, there are disorderly competitions in the wages of traditional proofing, such as low profit, even loss, and environmental pollution. The main consumables for digital proofing are printing paper and printing ink. The cost of printing paper has been significantly reduced. It will not be long before the price of digital proofing can be greatly reduced when it can be printed on plain paper. In addition, the cost of digital proofing system is low, accounting for The area is small, does not require special environmental control, does not require special management, digital proofing has many unparalleled advantages of traditional proofing.

As for the digital proofing system itself, different printing principles, different system configurations, and how different brand systems are evaluated, the method is exactly the same as described above, which is to see which kind of system proofs are closer to the effect of the printed sheets. In addition, the speed of the system (RIP time plus output time at the same resolution), maximum output resolution, performance of the system's proofing RIP and color management system, scalability, compatibility, and system cost Concerning the cost of consumables, the service life of the system hardware, whether it is prone to failure, and the after-sales service of the system, etc., this is not described in detail here.

(Li Jiaxiang)