Technical points of packaging and decoration printing image design

In packaging and decorating printing, the quality of the printing of images is increasingly required, and it is of great help in promoting the sale of goods. Beautifully printed images will give people a pleasing sensation and make people feel like they are in the real world. We know that the quality of printed products is constrained by all the factors involved in the copying process, from prepress design, production to the tone level of the original image, color tone and sharpness quality; color separation screening picture tone levels, colors, and Definiteness emphasizes the accuracy of the data such as copying and adjustment; the amount and stability of the conversion of intermediate points in the process of copying or releasing the net, printing, etc.; the ink layer density, dot gain value, or printing relative contrast data of the printing (or) proofing and The degree of control stability, the overprinting efficiency of each color ink layer, the tone evolution, color balance and gray balance reproduction; the performance of the printing paper and the operational adaptability; the chromaticity characteristics of the ink and its operation adaptability; the various operating procedures The printability of equipment, equipment, and materials, the quality of process operations, and the adjustment of data to be reproduced. Here, talk about the technical points of pre-press image design.

First, analyze the original

(1) Original density. It is the difference between the maximum and minimum density in the original (that is, the contrast). The maximum density that can be achieved for ordinary prints is 1.8. Generally speaking, all the density of a manuscript can only be reproduced in a range of 0 to 1.8 on white paper, and the density range of color reversal film can reach 0.05 to 3.0 or even 4.0. The gradation of the original must be compressed when printing and copying. Therefore, it is required for the original document to have a density suitable for plate printing. When the density range of the original document is too large, the sensitivity of the scanner and the extension unit to the portion beyond the density range decreases, and the color separation layer is flat. According to practice, the density of the manuscript ranges from 0.3 to 2.1, which is the most suitable when the contrast is 1.8. The color reversal film original density difference should be controlled within 2.4. If the original contrast is less than 2.5, a reasonable compression is performed when copying, and the effect is also satisfactory. However, if the manuscript contrast is larger than 2.5, even if the copy compression is performed, it will cause too many levels to be lost, and the level will be serious and the effect will be poor.

(2) The color cast of the original. Due to the limitations of the environment or light during shooting, most of the images recorded through the lens have a color cast. There is also an error in the process of shooting a color reversal film, and techniques such as developing and rinsing are not mastered, which can cause the original to color cast. The color cast of the original document usually has an overall color cast, a low-key cast color, a high-pitched cast color, and high and low-key colors (ie, cross-color casts). When considering correcting the color cast of the original, look at the whole. If you can't see a color cast, you can immediately process a color. This will cause Other color casts. The general requirement for manuscripts is that the difference between the three filter color densities is less than 0.2.

(3) Manuscript level. To measure the quality of copies, there are mainly three indicators: level, color, and sharpness. And mainly at the level. The level of normal manuscripts should be such that the entire picture is neither bright nor dark, high, medium, or low-key, there are many variations in density, and the tone is rich. However, many color reversal films have a lot of “boring” (ie, the overall reversal film density is too high, there is no high light spot, dark tone and intermediate tone are close to each other and lack of layers), and “flat” (ie, flat) The density of the darkest part of the reversal film is not high, and the density difference between high-profile and dark tone is small, the contrast is small, and “崭” (that is, the density of the darkest part of the reversal film is high, the contrast is large, and the level of the medium and dark tone loss is excessive). Such malpractices should be taken care of in prepress design.

(4) Original graininess and sharpness. Originality and granularity have a lot to do with sharpness. The thickness of the reversal film is also one of the important factors that affect the image quality. When copying, different scaling ratios require different particle sizes for the reversal film. The greater the magnification, the finer the original particles are. However, the phenomenon of coarse particles in the reversal film is very common at present. Under the 20× magnifying glass, the image roughness can be clearly observed, and the sharpness and the continuity of the tone of the image contour are affected. The thickness of the reversal film mainly depends on the type of particle structure of the photosensitive material itself and the processing of the photosensitive material. As for sharpness, color desktop platemaking systems and electric extensions perform color separations, which can use fine-grained emphasis on knobs or functions to enhance the sharpness of the image, allowing the copy to reflect originals more realistically. However, if the resolution of the original document itself is not high, even if a large number of knobs are used to emphasize the subtle level, a high-definition copy will not be obtained, and instead an embossed feeling will be generated. The sharpness of the image is related to many factors such as photosensitive material, jitter during shooting, resolution of the camera lens, illumination of the subject, and observation conditions.

(5) Platemaking requirements for manuscripts. For originals composed of black and white or colored lines, such as line (color) logos. It requires clear lines and no broken pens. The line thickness is appropriate. Fine lines cannot be eliminated after being copied and copied, and other lines cannot be exposed after they are enlarged. If the background color and the lines are all colored, the contrast of the two colors should be increased, which is beneficial for the photography to be divided into two distinct density levels. For leveled continuous tone painting manuscripts, it is necessary to approach color effects and physical effects. At the same time, the amendments should not be excessive, and the over-drawing of the screen will bring difficulties to the platemaking. For color reversal film manuscripts, it is required that the level of the main part (especially the high-medium tone part of the hierarchy) should be complete and rich, and the relative density range should be within 2.0. When the electronic separation process is used, the relative density of the original document can be slightly larger, but Should be controlled within 2.4. In the process of color reproduction, the reproduction of the memory color is sought to be true and accurate. The difference between the relative density of the neutral gray areas measured by the R, G, and B color filters is not greater than 0.03, and the luminance, the middle tone, and the dark tone are equal to each other. Achieve grey balance. For the particle size of the color reversal film, a magnifying glass having a magnification slightly higher than the reproduction magnification can be used for observation, and no obvious patch shape is suitable. The size of the original should be chosen to minimize the magnification based on the copy size. The magnification of the original should not exceed 6 times. The reproduction of color photographs and prints cannot be enlarged to ensure the clarity of prints.

(to be continued)