Discussion on Pre-press Graphic Processing and Group Edition Techniques (1)

At present, most county and city-level newspapers still use four editions and four editions, with a circulation of about 20,000 copies. Sometimes it is necessary to print a small amount of color newspapers at large newspapers. However, the same printing press is processed with the same software. The printing quality of the small color newspaper is a good time difference, and it is far from the hundreds of thousands of printed color newspapers. The reason for this is that the normal speed of the high-speed rotary belt is 9 to 13 meters per second, while the number of small color newspapers is usually only about 10,000 copies, and the colors have not been transferred to the best condition.

In order to solve this problem, on the one hand, it is required that the color of the staff of the machine tool be accurate and fast; on the other hand, in the pre-press processing process of the small color newspaper, the typesetting personnel should try to cooperate to make the color adjustment during printing relatively It is easier to speed up the color grading speed when printing in small newspapers.

Caipai prepress processing includes image processing, grouping, output, and plate making. The following discussion on image processing and grouping adjustments will improve the quality of small color printing.

Image color and level adjustment

The image plays a very important role in the color newspaper. In the printing of the newspaper, the image quality is good, and the coloring time can be reduced when printing.

1. Processing color images in RGB mode

RGB mode is the color mode adopted by the device based on the optical principle, it can express more colors, especially bright and bright colors.

The editing process of the image often goes through many steps. For example, if the contents of several images are combined together, since the original tones of the various components cannot be the same, they need to be adjusted. Regardless of the effect of image processing, the operator wants to make the picture as realistic and informative as possible. Since the color range of the RGB mode is much larger than the CMYK mode, when the image is processed in the RGB mode, a wider color space and more varied editing effects will be obtained. Although it must eventually be converted to CMYK, and there will certainly be a loss of color, it is always better to lose the color of the image than it was initially.

2. Image sharpness adjustment

Compared with high-end printing, due to the limited printing materials and conditions, the color newspaper has a lower image line number and a higher printing dot rate. Therefore, in the adjustment of small color picture images, it is necessary to use larger sharpening values ​​to improve image sharpness. .

From the screening process, sharpening has the effect of eliminating the loss of gradation that occurs due to screening. Therefore, sharpening is a necessary step in prepress processing. The degree of sharpening is related to the type and scaling factor of the original image. Usually, the sharpness of the human image is smaller, while the landscape draft may be larger; the larger the image, the greater the sharpness; the higher the magnification, the sharpening degree. The deeper it is.

3. Image level adjustment

The purpose of grading adjustment is to meet the printing requirements first. According to the characteristics of high rate of increase in printing outlets of newspapers, compensation for the increase of outlets will be concentrated in the middle area, that is, 20% to 60% of visually sensitive areas. The gradation of the original corresponds to the gradation that can be reproduced by the printing to make the image clear and real. Second, according to the manuscript content and level distribution, to ensure the accuracy of important parts of the tone, such as the character's clothes, face, etc. must be clear, the level of the difference should not be less than 15%. In addition, adjust the value of extremely high light or dark tone, not a large area of ​​network, the image tone adjustment is generally controlled between 2% to 95%.

4. Image color adjustment

The adjustment of image colors, also known as color correction, is mainly reflected in the reproduction of the original, rather than the color of the original itself. In the adjustment process, the color shift caused by the original or scanning is mainly corrected to ensure the accuracy of the color of the main part, and the screen effect and the final printing effect are also adapted.

Note that newsprint has a grayscale of 3% to 5%, and it is better to compare the standard digital prints with the proofs, open the original digital files, and compare the colors. At the same time, school color adjustments should be based on the information displayed on the information board, and cannot rely on the screen display effect alone.

5. Convert RGB mode to CMYK mode

The image used to print the sheet must be in the CMYK mode, so the image mode must be converted before the film is released. The image in CMYK mode is not bright in the RGB mode. After the conversion, the image should be checked first, and then the image should be output after determining the color shift. If you are not satisfied, you should immediately cancel the color mode conversion, and should not be converted back to RGB color mode, otherwise it will cause color loss.