With the development of computer-to-plate (CTP) in recent years, the industry generally believes that this technology is bound to replace the existing film-making process, but its development has encountered some obstacles. Because the film-making process using film can still provide some flexibility for manual modification, such as typos or partial plate changes. Direct plate-making is to use a plate-making machine to image directly on the plate. All the imaged data should not be lost, otherwise the full-page layout needs to be output again. In other words, compared to Ctfilm, CtPlate is a more stringent set of reliable digital workflows to properly handle the production process from the designer to the printing press. Therefore, the most controversial issue is not whether lasers can be used to directly create high-precision dots on the plate, but whether there is a set of approved digital workflows to replace the existing production methods, and the entire process needs to be considered Including: digital proofing, computer layout, flexibility to modify production efficiency, cost, trapping, and self-made film.
The following is an introduction to the requirements and technology of digital proofing.
Comparison between digital proofing and traditional proofing
Whenever the effect of digital proofing is mentioned, generally speaking, the traditional proofing will be used as a benchmark for comparison. Although the comparison is logical, it is often easy to miss the benefits brought by some functions attached to digital proofing. In the following, I will divide it into three major areas, including quality, cost and effectiveness, and try to compare the differences objectively.
Quality effect
Color simulation ability-Since the traditional proofing machine also uses ink to image, the color gamut that it can express in theory is very close to printing. In terms of digital proofing, some equipment can also use color inks similar to the ink composition, and the color gamut performance is also very similar to printing. However, the cost of inks and machines is very high (general equipment is between 500,000 and 1.5 million, depending on the size and accuracy). Other common color printers, such as inkjet or sublimation, can express a richer color gamut than printing inks, and the cost is very low. The key is how to use too rich color gamut to simulate the color gamut of printing inks, which depends entirely on the color management technology of which manufacturer is selected.
Outlet simulation capability-traditional proofing has an absolute advantage in this regard. Because they use the same set of film printing and printing. If the digital proofing is to simulate the net flowers, on the one hand, it will cost more than one million yuan to purchase high-precision equipment, but the effect obtained is difficult to be consistent with the real printing effect. For example, the precision of the digital proofing machine is 2000 / 3000dpi, and the precision of the phototypesetting machine is 2400 / 3600dpi. The net pattern created by the two is completely different. Most devices on the market that can simulate net flowers can only meet the visual requirements of customers.
Stability-Because the traditional proofing machine uses ink and adjusts pressure manually, the effect is very unstable. People in the industry have this experience: this is the same set of films that are taken out for proofing and the effect is usually different. Digital printing is automated imaging, which can be very stable, and such equipment is not difficult to find.
Reliability-The traditional proofing uses the same film as the printing, and the reliability is very high. The digital proofing system is designed according to the needs of pre-press process flow, we divide it into:
1. For example, the design proofing required by individual users who pay attention to cost and design performance;
2. Such as the output center that pays attention to production efficiency, the widely used RIP pre-proofing process;
3. If you pay attention to the requirements of data reliability, the RIP post-proofing process recommended by the industry.
In addition to human factors in the whole process, the most likely difference in operation is RIP calculation. The three methods mentioned above are available on the market.
Cost-effectiveness:
Investment cost-In this respect, traditional proofing is inferior to digital proofing. Because of the calculation of the same production capacity, if two sets of four-color proofing are completed within one hour, the investment of traditional equipment requires 4 sets of printing machines, matching printing and printing equipment, plus the required staff and The investment in a large factory is about 2 million yuan. The investment for digital proofing can be 2-15 million yuan, depending on the quality requirements, and the additional labor is close to zero. In terms of material cost, the cost of traditional proofing paper and ink is very low, and the higher proportion of the cost is the plate material and the potion. For digital proofing, a folio size is about 20-150 yuan, depending on the individual printer. In general, the return on investment of digital proofing (to a certain degree of quality recognition) can be much higher than traditional proofing.
Performance:
Production speed-on the surface, digital proofing imaging speed is faster. Common printers on the market can complete a folio of the same quality within 20 minutes. The traditional proofing, regardless of the size, does not include the imposition, printing and printing time, single proofing action, generally takes 30-40 minutes, but this is only a comparison of the production of a proof. When it is necessary to produce more than one color proof, the speed of the two is more similar.
A variety of simulation capabilities-the color gamut that most digital proofers mentioned above can express is richer than printing inks. The rich color gamut combined with good color management software makes digital proofing not only simulate the effect of printed matter, but also simulate other production effects, such as screen printing, digital printing, inkjet posters, etc., and even simulate The performance under the high-speed rotary printing machine can better meet the requirements of the increasingly diversified output in the market. The most common example is a set of advertising designs that need to be promoted through different media.
Multiple format capabilities-a complete digital proofing system, in addition to simulating the color effect of an output medium, can also automatically adjust the color of the image in the file for different output needs. The operator does not need to manually modify it. Can truly achieve automated workflow. The above two digital proofing features are lacking in traditional proofing.
Digital proofing options
Digital proofing can basically be divided into three categories:
1. Proofing design, designed for color layout.
2. Color proofing, aiming at the color effect.
3. Proofing the dots, and aiming at the color and net effect at the same time.
Overall, Color proof is the most comprehensive and highly selective, and it can achieve the best cost-effectiveness.
In fact, there are many types of color printers available on the market. The main imaging technologies include laser printing, thermal wax transfer, sublimation, and inkjet. The inkjet type can be said to be the mainstream medium and high-end products.
Introduction of digital proofing hardware:
Thermal transfer and sublimation technology: Thermal transfer technology transfers wax blocks containing pigments to special paper. However, the color space that this technology can cover is different from the color space of traditional offset printing. The proofing using thermal transfer technology is rough in appearance, and the generated dots are not consistent with the printed halftone dots; the sublimation technology proofing system uses a print head containing thousands of heating elements and a color belt containing CMYK pigments for proofing . The print head can produce 256 different levels of heat, so that the solid pigment sublimates into steam and condenses on the receiving medium. At the center of each point, the color is darker and the edge is lighter. When the four printing colors are printed, the four colors are fused together to form a continuous tone image; such equipment is expensive to use and uses The cost is on the high side.
Professional inkjet technology: Inkjet proofing system ejects ink onto paper to form an image. With the continuous improvement of hardware level, performance has been able to fully meet the needs of proofing. The equipment investment cost is also accepted by more and more users, but in terms of use cost, due to the need to use special paper and the necessary color maintenance work, it is feasible for professional system service providers to provide a full range of services to control costs. This practice is recommended by users in many countries.
Laser technology: This technology has high precision and can produce halftone dots. The specific technologies used are different. The general color expression is smaller than the printing color gamut, the system accuracy can vary from 1800dpi to 4800dpi, the equipment cost varies, and because ordinary printing paper can be used, users are often the first choice for color printing equipment.
Appropriate printers only provide hardware functions, and the most critical part of the entire proofing system is the color management software. In the topic of digital proofing, there is often a noun called "ICC PROFILE". This is actually a data file with a standard format, which is used to record the unique color gamut of different color output devices. Applying this "ICC PROFILE" in a digital proofing system is just a common procedure. What users need to master is how to effectively generate these data? Are users allowed to perform regular maintenance? This depends entirely on the technical level of service provider color management.
Software introduction
Our perception of colors in nature is determined by the following factors: the type of light source, how objects change reflected light or transmitted light, and our eyes' sensitivity to the changed light. The eye is one of the most important sensory organs. The principle of eye color and the principle of additive color mixing are consistent. When the red, green, and blue light in the external light stimulates the corresponding cone cells, the nerves generate electrical pulses, forming nerve excitement, which is transmitted to the visual center on the cerebral cortex, which constitutes a certain color. Different colors will have Different visual effects. The same color will have different auditory effects under different contrast changes. This is because the color contrast in the same picture will affect the brain's judgment of color. This is one of the important principles used in our color conversion.
First, there needs to be a way to measure and define colors
Visible colors can be composed of: hue, saturation, brightness. The hue is composed of the intensity of the one or two-color light with the largest proportion of RGB three-color light. When the RGB amount is equal, the color becomes unsaturated, and it looks gray or white, and the brightness is the RGB light wave that stimulates the eye to perceive the strength or wave height of the cell. These characteristics can be stacked from some "discs" to create a three-dimensional color model. What describes the change in the movement of the disc is that the hue moves from the bottom to the top to increase the brightness. Each disc moves outward from the center to increase saturation. This model is-irregular, because the eye's sensitivity to different colors is different.
Each device has its own color gamut space, some colors can be seen on the screen, but cannot be expressed by the output device. This is because the public space of the screen and the output device are inconsistent. Agfa CMS can connect and match two public domain spaces to solve the problem of color conversion. When using screen colors to simulate process colors, a method can reduce the unexpressible color gamut space to the expressible color gamut space, change the color of the entire surrounding environment, and use the relationship between the eyes and the brain to simulate different color gamuts. The effect of the time, so the latter has a better method, can make all color output devices have a certain color simulation capabilities.
Application of digital proofing
The existing digital proofing technology has been able to satisfy most of the general users. They mainly pursue speed, stability and cost efficiency. The performance of these three aspects of digital proofing is significantly better than traditional proofing. Examples of users mainly include general books and periodicals, printing of magazines and textbooks, etc.
For high-end users, the above three advantages can no longer fully satisfy them, and color quality is the most important requirement. But because of the strict requirements of these users, a layout usually needs to be modified many times during the production process, and many users of this type, such as advertising companies, have begun to use digital proofing as a test draft. In the process of modification, digital proofing has been used, and the traditional proofing is done again after the modification is completed. This alone can save a lot of cost of repeated proofing.
The above introduction hopes to provide some reference for everyone. The last thing to point out is that today's digital proofing technology has reached a certain practicality, but users must pay attention to the ability of software, hardware and services when choosing equipment, in order to achieve the most ideal results.
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