Color Printing Quality and Prepress Technology Adequacy (2)

b. Hierarchical correction

The calibration hierarchy curve is to compensate for the gradation that is compressed due to the setting of the black and white fields, to expand the dark tone, and to avoid dark divisions, to increase the contrast and adjust the ratio of high, medium, and low-key, to ensure the main level Correctly restore and increase the three-dimensional image. The correction of the image level should be analyzed and handled according to the type of the tone. It requires the operator not only to have experience, but also to have the ability to understand and process the image.

c, color correction

In the process of black and white field setting and level compensation of the image, it will inevitably lead to changes in its hue. In order to improve the color effect of the image and adapt it to the printing conditions of the newsprint, color correction must also be performed.

Color correction is to do the gray balance processing, but also according to the newsprint itself with grayscale and color cast, printing color purity reduction characteristics, in the color purity to be properly handled.

For a picture with a certain color as the basic color, the basic color can be appropriately exaggerated and given enough to make the printing effect more prominent.

In the main body color, the amount of the opposite color should be reduced as much as possible, for example, reducing red in red, red in green, and yellow in blue to enhance its purity.

On the basis of not affecting the overall gray balance of the image, local color can be corrected by using regional processing methods, such as the face of a person, the substrate of art and calligraphy works, and the sky and green space in the landscape image. In an image with a gray tone as the main body, properly refining the local color enhances the overall color of the image.

Through the discussion of adaptive processing of image color separation, it can be seen that there is a big difference between the color image printing image processing and general color printing products. For general color printing products, under the condition that the quality of the original document is good, as long as the correct setting of the scanning parameters can be done, generally no more processing is required for each picture.

However, in order to adapt to the process conditions for the printing of color papers, it is necessary to focus on the improvement of the sharpness, the selection of the gradation range, and the improvement of the color purity in the image processing, which brings about the problem of appropriate selection of the original. It can be said that the image processing of color newspapers is the result of the combination of technical control and art processing under the limited process conditions.

Therefore, in addition to the standardized data and certain experience accumulation, the adjustment of color also requires the operator to have certain color theory knowledge, as well as the ability to understand various types of images and artistic processing capabilities.

Due to the different aesthetic requirements and design styles of the newspapers, the image processing methods of the newspapers are also different. At present, there are basically two styles of image processing on domestic color newspapers.

One is to enhance the sharpness of the image by means of a large contrast, with emphasis on the planar effect of the image color, and to increase the purity of the color in the high and middle areas as much as possible, rather than pursuing delicate levels of change, so that the image is clear, vivid, and bright. This style is easy to express the brisk, lively and colorful visual effects of the entertainment layout.

The second is to focus on the image level performance, try to reproduce the three-dimensional image of the main body, the pursuit of rich, rich and powerful visual effects. This style is easy to express major news pictures and works of art. If it is combined with a thick substrate and eye-catching headlines, the visual impact of the layout can be enhanced.

Therefore, in order to establish and maintain the style characteristics of different newspapers and different layouts, it is necessary to achieve mutual communication and cooperation between layout designers and image processing operators, and learn from each other in terms of professional knowledge.

4 automatic color management technology

Automatic color management technology is a new technology that has been developed in recent years in terms of color description and automatic conversion. It describes the printing conditions through the system equipment and related software, and automatically converts the color so that the screen display and proofing effects are as close to the actual printing effect as possible.

Automatic color management technology is more practical in color newspaper printing. It can achieve screen color and color proofing similar to the printing effect of newsprint. It is for editors, layout designers, advertisers, and image processing operators as well as color printing. The operation provides a simple and intuitive way of monitoring. It can not only solve the difficult problem of newsprint printing, the difference between the screen effect or the proofing effect of coated paper, but also suits the special requirements of a one-time successful newspaper production. The equipment, software, and technology in this area are currently being improved.

2. Plate making

At present, most of the newspaper printing companies in China still use the traditional technique of splitting and printing in the form of a color separation sheet as a master. Its quality control is mainly in the process of outputting color separation films, imposition and printing.

1 The quality of the separation

The color separation film is the final product of the image scanning and text group edition, and is the basis for printing. The quality of the color separation film is generally determined by the density value and the gray value, and its quality control is mainly reflected in the following aspects.

• The settings of the laser imagesetter match the system equipment and operate normally. In order to ensure the stability of the laser, the laser head should be tested and corrected regularly.

• The liquid concentration and temperature of the punching machine are normal. According to the performance of the color separation film and the liquid, set the value of the developing and fixing parameters, and test with the test strip and the ladder at any time, and at the same time, perform the daily cleaning and maintenance of the punching equipment to prevent the turbid materials from separating the color film. Dirty.

• The performance of the separation film and the liquid itself is stable. In order to meet the requirements of the timeliness of newspaper production and ensure the stability of printing quality, variable factors should be minimized in the use of raw materials, so that the use of raw materials is relatively fixed.

In addition, the color separation sheet is susceptible to scratches due to foreign matter during the operation and transmission of the device, and the transmission parts should be cleaned and replaced periodically.

2 imposition

In the case that the advertising manuscript cannot be completely digitized and the laser photochromic separation sheet is mainly composed of four different parts, the imposition of the process link is indispensable. Imposition should be positioned, fitting accurate and error-free. For color newspaper printing, due to the limitations of the accuracy of the rotary printing machine in terms of multicolor printing, it is required that the imposition of the imposition should be more accurate.

In order to reduce the dirt on the layout and increase the printing resistance of the PS version, many newspaper companies use the negative graphic plate making process, which not only brings difficulties to the positioning and fitting of the color newspaper's imposition and advertisement inserts, but also it is not easy. Found mistakes. Newspapers are politically oriented and highly time-sensitive products. Mistakes, misspellings, and reversal of orders will cause incalculable losses. Therefore, in addition to solving the technical problems in this process, it is more important to improve the responsibility of the operators and to strengthen the accountability system for the control sample inspection.

3 printing

Shaiban is the last process in the prepress process, and it is also a key process for color quality printing control. There are many factors that affect the quality of printing. According to the characteristics of printing in color newspapers, on the basis of correct exposure, the problem of improving the printing resistance of PS plates should be emphasized.

According to the characteristics of small print range and high dot gain rate in color newspapers, it is necessary to properly control the exposure amount so that the development time, the concentration of the drug solution and the temperature can be matched with each other, and this is especially important for improving the quality of the dot network. In this regard, the quantitative control of various variable factors must be implemented so that the photosensitive part of the PS plate forms a good graphic area and a "strong" network point through normal chemical reactions.

Newspaper printing is generally dominated by "long-run" games. The rough paper of newsprint and the accumulation of paper hairs can cause problems such as graining and dirtiness. In printing, in order to reduce the plate change and increase the time efficiency, the quality of the PS plate itself is required to be higher. The PS plate should have a high print resistance, good stability of the photosensitive layer, uniform coating, high plate base strength, and uniform thickness. In addition, moderate baking can also improve the PS plate's resistance to printing.

When printing on a medium-sized machine or a mainframe, one version of the drum requires 2-4 PS plates. The orientation of the PS plate is slightly deviated, and part of the plate is difficult to register. Therefore, the PS plate's cutting size error, bending operation, and slight error in the plate-up operation will affect the overlay accuracy and should be paid special attention.

4 direct plate making technology

With the development of prepress technology, direct plate making (CTP) technology has become an inevitable trend for prepress technology development for newspaper printing. It reduces photocopying, punching, imposition, and other aspects of the traditional platemaking process, reducing the variable factors that affect the quality, and plays an important role in controlling the quality of the printing plate and improving the timeliness. This has been discussed in many ways. Repeat again. It should be noted that while introducing and introducing new process technologies, new control factors affecting quality will be encountered, and the traditional plate-making process management will also change accordingly. It is necessary to research and establish new process conditions in a timely manner. Management methods.