Gray balance guides the stability of newspaper printing

Printing refers to the process of bulk copying textual information in an original document on the principle of being faithful to the original or higher than the original. The physical and chemical properties of the four inks C, M, Y|K determine the quality of the printed matter. In particular, the respective color performance and color purity of the four-color inks will directly affect the color of the printed image. The plate-making staff should first take this into consideration when they are engaged in image scanning and color separation. It is important to understand what color the four-color inks prefer when printing. In theory, the equivalent of C, M, Y superimposed to generate ash, but because the ink contains impurities, such as C ink contains a certain M, Y, the ink's color cast to achieve the gray balance of C, M, Y value is not Wait.

Gray balance is one of the most important contents in the theory of printing and copying. It is the basis for the existence of all colors in printed images. No matter what color is changed on the basis of the gray balance data. We prioritize the gray balance of the printing ink and use it to guide the scanning of the image, which is a guarantee of high quality prints.

There are many factors that affect the gray balance data, such as the brand name, number, and the conditions for proofing and printing of paper, proofer, and printer. You can consult the proofing company and find the company's gray balance data to guide your own image input processing work to ensure the print quality. You can also test your own, to obtain a set of data, but the premise is to ensure the stability of the proofing conditions, such as the same field density of four-color ink, paper, ink, equipment and other performance indicators are unchanged, while ensuring the linear arrangement machine Normalize. Then, according to the data of C, M, and Y listed in Table 1, a gray ladder is made in photoshop and a proof is taken out. Gradually check the gray scale. If the gray scale is warm red or partially warm red after proofing, it means that the data of M and Y should also be reduced. After correction, a proof is taken out until the proofs are gray. The ruler. Record this set of C, M, and Y data as your own gray balance data.

Table 1 is the gray balance data for a set of inks.

If a neutral gray is slightly colored, it is easy to judge with the eyes so the gray balance is the best method to determine whether the printing color is balanced or color shift. Gray balance is the reproduction of the tone in color image printing, color reproduction and The scale of dots and inks in color printing can represent the degree of color reproduction of the whole picture from light to dark in color printing and copying, and it is also a means to control the quality of printed products in printing production.

There are a lot of gray balance data, readers may feel very boring, not easy to remember, in fact, as long as you understand the general laws of these data is not difficult, such as in the vicinity of the middle tone, C data is 7% larger than M, Y ~ 9%, high-profile office is 2% to 4%. Gray balance is the cornerstone of color, and all colors can be explained from the gray balance data. What is the color of C30M25Y34? If you do not understand the gray balance data, it is difficult to judge the color at once, unless it is very skilled and has many years of work experience. With gray balance data, the problem becomes very simple. The C40M33Y34 is a gray block. The M value is now 25, which is 8 percentage points less than the gray balance data. The complement color of magenta is green and the lack of magenta is equal to the proportion of green. Therefore, the color block is green, and because the difference between the three color data is not large, it should be grayish green.

Scanning is the first step in influencing the color reproduction. In order to obtain a stable and reliable scanning quality in the desktop system, the scanner must be calibrated to compensate for the deviation of each component. The basic tools for calibration are silver-free ladder scales or reflective color scales (including the 22-step gray scale). The basic standards for calibration are tone reproduction and gray balance.

Print copy can be decomposed into a copy of the tone level, color, and sharpness of the original. The reduction of color relies on the reproduction of the tone and the restoration of the gray balance. Therefore, when the image is scanned, the tone and gray balance are taken into account, which lays the foundation for the entire image reproduction. The gradation of an image refers to the range of light from dark to dark in an image and the distribution of light between light and dark. Electric extension processing is divided into two steps. First, the high and dark points in the image are determined. Secondly, the scanning curve is selected. Referring to the motor, we must select the white field and the black field during operation. Level as a white field, level 22 as a black field, to scan RGB mode as an example, the first level of data set between 250 ~ 255, 22nd level set to 0 ~ 5. In the middle of the steps to achieve evenly opened, 11th level control at 128 or so. Different scanners and different scanning software, the method of adjusting the black and white field is very different, the user needs to find out the change rule of his own scanner, control the data, for the adjustment of the middle tone, almost all scanners are the same, Adjust the gamma value.

Gamma values ​​are often common. Such as the gamma value displayed on the screen, they all represent the relative relationship, which is the curve between the black and white fields, that is, a certain curve on the extension. Once the black and white field and the curve are determined, the digital image's value is immediately determined. Therefore, we change the gamma value, which changes the tone of the digital image.

Whether or not the gray ladder can be faithfully restored has an important influence on the reproduction of colors. Looking at the quality of the work, it is often necessary to first look at the gray reduction situation. When the gray balance of the image is controlled during scanning, the color part can be guaranteed. Not color cast. The gray balance of the image is accurate and one of the prerequisites for color separation. Here, we adjust the RGB data of each stage using the 22 gray blocks in the gray scale so that the three remain approximately equal and the maximum error does not exceed 58 (this corresponds to 2% dots in the print). When adjusting, it is often necessary to adjust the high, dark, and midtone Gamma values ​​of the three channels of RGB in a single channel.

With regard to calibrating the scanner, we have adopted a push-back method. Because we are using a standard gray scale, the density range and gray balance can meet the requirements. If a part of the scanner has a big problem, for example, the red signal is too sensitive and strong, because the digital image after scanning must ensure the gray balance, Inevitably reduce the red intensity, use a special printing plate, the factory printing newsprint requires 3% of the small outlets to keep, 2% of the outlets drying out, 98% outlets do not stick to death, thus compensating for the imbalance of the three channels, To achieve the purpose of calibration.

Source: Printing Technology