Connection between Processes and Image Quality (I)

First, the connection between processes

1. The need to transfer information between processes. A set of sub-packaged films only plays one role in the multi-color copying process. The final effect of the image depends on the printing of four-color inks on paper. For best results, the various stages of replication should be carefully controlled, and the results of the controls must also be passed on to all other people participating in the replication process. For example: In order to get consistent results, printers must optimize production conditions and control; plate-making workers must maintain the quality of images on plates. It is also important that color separation personnel and proofing personnel must understand the control tolerances of platemaking and printing in order to produce color separation films and samples suitable for other production processes.

The printed products are different, and in order to obtain the best results, they must be carefully planned, especially for multicolor printing. In order to properly arrange and achieve high standards of color reproduction, the delivery of color information is the most fundamental requirement. Most color separation workers, plate makers, samplers, or printers can do a good job, but they can't do a good job in isolation from the color transfer of other processes. The opportunity of color transmission destruction is more than other aspects of production in the color reproduction process because of two aspects. First, the complexity of color reproduction itself, each step of production requires very precise and strict quality control in order to obtain The second is that due to the unbalanced nature of technological development, for example, the technology of electronic color separation and its related technologies is almost developing rapidly, while areas such as printing plates and printing presses continue to advance. Compared with the image processing technology of the full-page imposition and color desktop system, it is still not adaptable. As a result, as color separation personnel, they learn more advanced theoretical and practical knowledge than others, and color separation personnel have an attractive operating environment that is not available in other processes. In order to obtain the best results, color separation personnel often create their own standards and set production conditions without information exchange, so that printing and printing staffs meet such goals; on the contrary, color separation personnel are often subject to quality problems. Recrimination of other processes is a common contradiction in production. The lack of information exchange in each process is one of the reasons for the destruction of color transmission.

2. Color separation personnel should have information on Li Jia.

1 printing paper. The quality of paper is closely related to the quality of the final copy. Separators and others in the prepress process must know the type of paper used to print the product. Whiteness of the paper, absorption characteristics of the ink, smoothness of the surface, etc. are closely related to the quality of the printed matter and reproduction of the prepress image. In order to achieve the color balance between the color separation sheets, the color rendering effect of the ink on the paper surface must be taken into consideration when performing the correction and level adjustment. For example: A set of color separations made for smooth coated paper is not suitable for rough surfaced paper. Similarly, proofing should also use papers with similar hue and structural characteristics in order to simulate printing effects. Separators should quantify the control of color separation equipment based on the effects of different paper surfaces in order to obtain the best results.

2 ink. There are many inks with different hue characteristics. In order to achieve the best effect of color separation, color separation personnel should adjust the subcontracting equipment according to different ink types, but a wide variety of inks may cause confusion because color separation personnel and proofing personnel are satisfied. The effect is to constantly change the separation conditions. Therefore, a group of inks of the hue standard should be adopted as much as possible. Once there is a change, the relevant personnel should be informed immediately. This kind of information transfer can reduce problems related to production personnel. Using a standard set of inks also makes it easy to match proofs and printing.

3 ink thickness. The color intensity of the ink is related to the thickness of the ink layer printed on the paper, which is controlled by the printer. When the thickness of the ink layer is different, the light reflected by the paper surface will change, and the effect of printing and proofing can be controlled by measuring the reflected light. If the densitometer reading changes significantly, the necessary adjustments must be made to correct the printing condition. However, different densitometers may respond differently to reflected light, resulting in different readings. Therefore, printing, proofing, and color separation personnel cannot use only density readings to convey color information unless they previously calibrated each other to the densitometer.

4 outlets increase. It is not possible for the halftone dots to pass equally between processes because dot coverage is affected by many complex optical and mechanical factors. For example, the internal reflection of paper and ink, printing plate, blanket, paper type, printing pressure, roller lining, ink layer thickness, ink viscosity and fluidity and so on. Obviously, in order to obtain consistent printed images, dot gain must be controlled to a certain extent and the printing conditions must be standardized. If the colors are fluctuating during printing, four-color printing will be unreliable. For four-color printing, the difference in dot gain between color and color must not exceed 4%. In order to compensate for the influence of the aforementioned factors, the color separation and proofing personnel must have information on these variables in each production process. Density meters can be used to measure and evaluate dot gains. For example, if the density of the dots does not change during the printing process and the dot density changes, then it can be considered that the dot coverage has changed.

5 gray balance. As long as the ink characteristics, ink layer thickness, and dot gain are defined, one of the most important parameters for controlling color reproduction is a group of yellow, magenta, and cyan inks that are produced from white to black in a series of neutral hairs and blacks. The proportions of components and components are related to the increase in the thickness of ink layers and the dot gain of each color. With the advent of CCR, the neutral color can be partially replaced by black ink, but the gray balance is still an extremely important parameter. The gray balance deviation will lead to the unbalanced reproduction of each color, causing a significant color cast. . In order to control the color during printing, the printer can visually judge the neutral tone of the three-color synthesis. If the initial relationship between the ink is destroyed, the neutral surface will have a color characteristic, and the worker will adjust the machine according to the direction of the deviation. .

6 overprint and color sequence. Ink overprinting means that the wet ink is laminated on the printed ink layer. The ideal thickness of the overprinted ink layer should be the same as the thickness printed on the paper alone. However, the pre-printed ink cannot completely accept the wet ink layer, resulting in the pre-printed ink exhibiting an advantage in copying. Different printing orders, the color effect of overprinting may be different. For example, when yellow and magenta are first printed, the image will be reddish. If yellow and cyan are printed first, the printed image will be greenish.

The ideal ink is transparent, printing color sequence should not have any effect on the printing effect, unfortunately the ink chain material is not pure, it will scatter light, so that the ink to a certain extent, produce opacity. As a result, different color sequences may also cause different replication effects. To maintain color consistency, these parameters must be controlled and prioritized.

7 print control. exposure. Development and other factors will affect the dot area of ​​the printing plate. Standardization is the control of the quality of the printing plate.

Keys, color separation personnel should understand these control specifications.

3. Electronic color separation quality control. The electronic color separation device is a high-precision color separation device, which allows the operator to flexibly carry out his own intentions. Different operators will significantly different the productivity and color separation quality of electronic color separation, and the problems closely related to quality and productivity are mainly It involves the following aspects:

1 Establish standard working conditions for color separation equipment. The purpose of establishing a standard working condition for the separation equipment is to ensure the quality of color separation and ensure high productivity. This involves the following aspects.

First, according to the emulsion characteristics of the original film and the initial adjustment of the electronic color separation equipment according to printing conditions such as ink, paper, and printing press, these adjustments are kept constant, and then they are adjusted and adjusted by the gradation control to achieve the printing halftone. The best dot coverage value for the ruler. If the first set is the ideal tone reproduction curve, the maximum dot gain value is in the 50% dot area, and the dot gain generated by the current printing conditions is 10% larger than the normal value. The mid-tone coverage on the curve is reduced by 10%.

The electric extension is then programmed according to a pre-determined value so that it can achieve the gray balance correctly.

After completion of the tone copy adjustment and gray balance adjustment at the electric extension, the color adjustment is performed immediately, and the standard adjustment of the electric extension is completed.

In order to check the adjustment effect, color separation can be used on the electric extension to separate the color and use a color proofing system that can match the final printing result to proof a set of color separations; the proofs and color originals are discharged together for observation and analysis. If you are sure that the gray balance adjustment is correct, then check the correctness of the gradation copy. If the gradation copy is also correct, only a small adjustment is needed to match the color proof to the original color.

The above process is repeated a number of times until satisfaction is achieved. The result of this adjustment is a standard operating condition that is consistent with the characteristics of the film emulsion.

It should be noted that the human eye has poor memory of colors. When you compare proofs and manuscripts, you should try to keep them close to each other and place them in the same field of observation. This visual evaluation method and the technology that optimizes the output of the electrical extension are widely used at the production site.

According to the previous description, it seems that it takes a lot of adjustment time to make a set of separations. What is done in front is to establish the best standard working conditions for the separation equipment. When the manuscript is later obtained, the operator only needs to find the bright and dark positions of the manuscript for supplementary adjustments unless there is a different requirement for tone reproduction. There is no need to re-adjust the color correction. Most manuscripts only need to pass a suitable bright tone. Midtones and shadow adjustments can be used to perform color separations, and this work is now done automatically by the preseparation system.

2 Establish ideal midtone dot value according to the characteristics of the original. If the characteristics of the original are different or there is a special requirement for tone reproduction, only a slight adjustment to the standard adjustment conditions is required. The method of change is the same as the adjustment method that adapts to the printing conditions, and the curve is shifted from the midtone dot size to correct the incorrect contrast in the original (Figure 3-11).

Fig. 3-11

For example, for an overly-thin, overly-thin manuscript, where the tone level is rich and there is almost no shadow, you need to increase the midtone and 1/4 tone to increase the bright contrast. Such shallow manuscripts tend to have a low contrast in brightness adjustment and need to increase the tone adjustment detail by increasing the midtone adjustment value. When increasing the midtone adjustment value, the 1/4 tone is automatically improved, but the amount of lifting is less than that of the intermediate adjustment.

Another example is the lack of exposure of thick stuffy manuscripts. Most of the important details in the dark tone area are barely bright. In order to increase the dark tone contrast and details, it is necessary to reduce the midtones, and to reduce the midtones to increase the total gradient of the dark tone. It may also be necessary. Decrease 3/4 tone. Decreasing the shadow by the background removal method does not increase the detail of the dark tone, it will flatten the dark curve and lose detail.

3 tracking and adjustment of the quality of electricity. After a long time working on the extension, the output of the optical system has changed, but the amount of change is very small and often cannot attract people’s attention. For example, the lens may become stranded, which may obscure details and some color control loops may drift. So within a certain time interval, such as a month, use a standard manuscript for a color separation operation. Compare the proofs with the previous proofs. If you can visually see the difference, it means that you need to establish a standard adjustment again.

4 scanning analysis of the original. Analyzing the manuscript is a job that requires experience. The electricity subdivision personnel must evaluate the manuscript and determine the method of replication in combination with the customer's idea. If this work allows different operators to do, there are often many points of view. It is best to let experienced and good separation personnel make judgments. This work can also be done by the computer, that is, using a pre-scan analysis system. This system will use the original image information according to the scanned document density, dark density, exposure, color content, tone distribution, contrast and bias. The color condition is evaluated, and accurate adjustment parameters are calculated accordingly, and the color separation device can be adjusted within a few seconds. Conventional electronic color separation or desktop systems can configure such systems or functions.