Analysis of Image Design Techniques in Packaging, Decoration and Printing (I)

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.

Second, the lack of manuscript processing

1. Color cast processing method

The true condition of different original tones can be observed more intuitively from the measurement of the three-color density contrast of the original and the depiction of the tri-color density curve. The most popular method of dividing the density range in the color printing reproduction process, which divides the entire density range of the original and the replica into four segments, ie, the entire density range between the highlight spot (white field) and the dark tone spot (black field). Divide into bright (also known as high-profile), middle tone and dark tone of the three segments, and the area less than the high light density is called extremely high light. There is also a five-segment density range, that is, in the above-mentioned four segments, an area with a darker density than the above is also called extremely dark. In the analysis of the original color quality, if the original three-color density and contrast are basically the same, indicating that the original is not color cast, the tone is basically normal. If the tone is complete, the levels are rich, and the distribution is reasonable, even if the total contrast is slightly different, it can be considered a normal manuscript. The color reproduction can be corrected with the normal color error data, and the emphasis is on the reproduction of the tone level. If the three colors of the original document have different densities, it means that one of the colors is biased, and when the contrast of the three color densities is substantially equal, the color is balanced, which is caused by the color fog. This partial color draft, the general tone level is also better, you can change the color separation picture high and low profile three-color dot record settings, and with the adjustment of the level adjustment to achieve full gray balance to eliminate image color cast. However, it is better to design a hierarchical replication curve that adjusts the balance of three-color gray according to the three-color density curve, so that the tone of the full-tone tone can be uniformly corrected. If the difference between the highlights of the original three-color density is relatively large, the three-color density of the dark tone is nearly the same, and the color cast is mainly displayed at the end of the high-profile region, which is unfavorable for high-level reproduction of the image. Although this kind of color cast can directly use the original color shift highlight point as the white balance and input calibration of the color separation machine, the input balance of the color separation machine is changed, but the color correction signal is also changed, and the high light to be retained is retained. Color also lost, data

Often inaccurate. It is better to design the tri-level version of the level reproduction curve based on the tri-color density curve derivation, change the recording setting of the high-light tri-color dots of the color separation image, and correct the high-order color cast accurately. If the original highlight three-color density is basically the same, only the dark tone of the three-color density is different, the density contrast is not equal, in the dark tones show a significant color cast. The tone level is slightly lost, and the high-level level is normal. You can change the color separation picture dark tone three-tone dot record settings, or add a color full tone background removal (only for mixed complex color role), to eliminate the tricolor record picture in the dark tone side of the color cast. It is also preferable to design a three-color hierarchical replication curve that adjusts the gray balance by deriving the three-color density curve, and correct the color cast with accurate data. If the original tri-color density curve is crossed, the image is high-profile biased to one color, and the dark tone side is biased to another color, which is the cross-color cast caused by the three-color balance of the photosensitive sheet itself. The levels of tone at all levels are not good. It is not easy to correct the color cast on the scanner or the color separation machine by changing the three-color level adjustment and recording settings. It is necessary to derive accurate adjustments based on the three-color density curve. Gray balance three-color level replication curve, guide its three-color level adjustment and record setting, can make its copying effect slightly improved. Differences in color cast density of 0.2 or more are generally difficult to correct. When faced with a more serious color cast, the color difference of the three color differences more color original, in addition to measuring its high light, dark tone density meal, it is best to add the middle of the original tone of the scenery should be neutral gray three-color Density, the color draft, needs to be based on the tri-color density curve, deducing the design to accurately adjust the gray balance of the three-color hierarchical replication curve in order to adjust the color cast on the desktop system and the color separation machine. However, when dealing with the color cast of the original, care must be taken to carefully analyze whether the image is really color cast, because some are artistic effects that the author intentionally created. For example, in backlighting photographs, due to the stress of backlighting works, the color tone changes greatly, and various color tone patterns can be formed. Some are based on warm colors, while others are based on cool colors. However, it must be taken into consideration that some shades of the backlight photographs look somewhat distorted. In fact, the author deliberately pursued it. Therefore, this type of manuscript cannot be considered as a color cast. Therefore, the manuscript should be carefully analyzed and fully reproduced during copying. Understand the author's creative intentions and accurately grasp the keynotes of the screen. The manuscript with obvious color cast not only requires very precise measurement of the three-color density data, but also needs to take into account the correction of color cast when color separation is performed. The tri-color version of the original copy must be used to balance the tristimulus of the original color tone. To be adjusted, redistribution adjustments must be made to their levels, which should be the focus of operations. The correction of the color reproduction error is based on the adjustment of the three-color version to the data of printing gray balance. Due to the change of the color shifter color signal, the color correction data will also change, which needs to be based on compensating the color shifter to eliminate the color shift after the color shift and chromatographic color combination data, and finally correct the color error.