Analysis on the Related Essentials of Gravure Printing Technology
First, the electronic calibration should be combined with the printability Plate-making serves printing, and printing is the standard to test the quality of plate-making. At present, the printing conditions of domestic plastic gravure printing industry are far from the production conditions of plate-making industry, resulting in the printing samples of some products failing to achieve the effect of plate-making samples.
There are two main reasons for this. First, due to the cost constraints, printing plants often use cheap printing inks. These cheap inks have poor stability, and neither the color saturation nor the transfer characteristics of outlets can meet the standard of plate making and proofing; Secondly, the production environment of printing workshop is poor, and most of them can not reach constant temperature and humidity. Gravure printing ink uses benzene and alcohol volatile solvents, and the transfer effect of shallow screen in printing process is closely related to printing environment. With the high ambient temperature, the solvent volatilization speed is accelerated, the adaptability of ink viscosity is narrowed, and the small net holes are easy to dry. If the humidity is too high, the moisture in the air will increase, especially in summer with high temperature and humidity, the rapid volatilization of solvent will take away a lot of heat, which will make the moisture in the air enter the ink tank, thus making the solubility of ink worse and affecting the transfer of ink and the reduction of dot. We have learned from quality accidents in this area, such as low temperature in winter, and 1% of outlets in pure white areas can be restored, which affects the transparency of blank areas; In the high temperature season, 5% ~ 6% of the dots are lost, resulting in weak color and lack of layering in the bright area of printed matter.
Therefore, the electronic calibration should be personalized with the printability. Integrating the ink characteristics and printing conditions used by printing plants, several digital ink characteristic curves are drawn in different categories to adapt to different printing suitability, which is also the key for plate-making plants to win the market. In summer, the ink transfer of shallow screen is poor due to high temperature, especially when the blank area in the direction of shallow screen facing the knife is large, which will also affect the ink transfer in shallow screen area. A shallow screen coloring curve can be set up to compensate for the loss of shallow screen. This monson starts at 3% of the outlets and ends at 40% of the outlets. At the same time, the outlets on this monson are moved up by 2% ~ 3% on average, and the curve is as smooth as possible. It should be noted that the monson should be loaded after the digital samples meet the calibration requirements.
In addition, gravure printing technology emphasizes that the color concept of three primary colors is related to printability. Most foreign documents are designed by GCR technology, and the bright TINT is often black and complementary colors, which is no problem in offset printing. However, gravure printing technology is easy to cause uneven color leakage and affect the reproduction quality due to unstable factors such as poor transfer of shallow screen and easy collision with screen. Therefore, it is beneficial to improve the printability of the complementary color plate by calculating the amount of black color in the color image in the complementary color plate, which is also the importance of GCR process conversion as we mentioned earlier.
Second, adjust the manuscript of the character When adjusting the original manuscript, special attention should be paid to the facial skin color of the characters, because the printed facial skin color will lack delicate hierarchical contrast and color change due to the influence of the dot reduction characteristics of gravure printing process. Therefore, considering the characteristics of gravure printing process, we should pay attention to three factors when adjusting this kind of manuscript.
1. Pay attention to the soft level effect The reproduction characteristics of gravure printing technology, such as high-gloss level easy to level and dark-tone level easy to merge, determine that the reproduction concept of soft level should be emphasized when expressing people’s facial skin color, and the high-gloss level and dark-tone level should be appropriately moved to the middle tone direction with ideal reproduction characteristics, so as to improve the reproduction characteristics of high-gloss level and dark-tone level.
The main color outlets of the yellow and magenta versions of the characters’ faces are generally not less than 10% ~ 12%; In the part connected with the middle tone, the outlets of the yellow version and magenta version are generally about 20%, so as to make the skin color transition natural. Green Edition generally does not directly disconnect the network, but retains 1% ~ 2% of the technological network points, and the hierarchical contrast should not be too large, which is helpful to improve the hierarchical hard mouth formed by the disconnection of the network. Portraits on cosmetic bags and food bags are small in size, and the printing level is easy to level. It is necessary to reasonably strengthen the level changes of basic colors of yellow and magenta versions, and strengthen the level contrast between bright and middle tones. The network points of the light-receiving parts of the characters’ faces should be well grasped, and the level transition should be uniform. For those manuscripts with poor facial light sense, they should be decorated and brightened, but they should not be distorted. Characters’ faces The color of the dark side should not be too heavy. According to the color change of the dark side of the original manuscript, deal with the dot relationship of yellow, magenta and cyan, be naturally dark, not dark, and connect the level transition between the dark tone and the middle tone. The shadow outline of the face should not be overemphasized to prevent the facial expression from being dull and inflexible.
2. The application of color versions in skin color reproduction Yellow plate is the basic color plate for skin color reproduction, and the relationship between warm and cold and color changes in skin color should be solved by yellow plate, so it is required that the yellow plate should have a few layers, and the dot of highlight part should be smaller than magenta plate. The magenta version is the main color version for skin color reproduction, with soft and delicate layers, and proper touch-up of lips and cheeks. Green plate plays the role of balancing color, suppressing brightness, showing the relationship between light and shade and outline level. Black version is not advocated in skin color reproduction, because black ink is coarse in grain, poor in transparency, inaccurate in digital sample simulation, and difficult to grasp the amount of contrast. It is generally required to replace black components in skin color with cyan to improve the dot transfer characteristics of green version.
The facial skin color of the original manuscript is ever-changing, and the contrast amount of different versions is different, but there is a certain color relationship among the three primary colors in the skin color, and the following empirical values can be used for reference by power supply personnel. The hue of the forehead part of the character’s face is slightly warmer, so that the dot size of the yellow version should be 5% ~ 8% larger than that of the magenta version. The skin color of children and young women tends to be white and ruddy, so the dot sizes of the yellow version and the magenta version are similar. On the cheek, the dot of magenta version is 5% ~ 10% larger than that of yellow version. The lining volume of the green version generally starts from 20% ~ 25% of the outlets on the magenta version, and the white color of the white people is white and blue, so we should pay attention to the balance relationship of the green version.
3. The application of black plate should be combined with printing characteristics The overprinting accuracy and dot gain of gravure printing process affect the clarity of layers and the expression of characters. Generally, the dots of yellow, magenta and cyan in hair, eyes and eyebrows should be removed and modified accordingly. The amount of lining is generally about 30% ~ 35%, and the charm of these parts is mainly expressed by black. In the process of color conversion, the inherent color distortion of whites and pupils should be avoided, and the black tone of black eyeballs, canthus and eyebrows should be widened and extended moderately. The black level in hair should be enhanced by contrast, and the network points in the darkest place should be controlled to be 90% ~ 95%, while the black network points of eyes and eyebrows should decrease according to the charm of characters.
Third, improve clarity Clarity is one of the important factors affecting the quality of printed matter, which has three meanings: first, the clarity of image edge outline, second, the clarity of picture outline and lines, and third, the subtle contrast between light and shade and the discrimination of image details. In the process of copying, the manuscript has undergone scanning and color separation, especially the off-line scanning of printed matter, and the increase of dot and misregistration in printing will affect the clarity of printed matter to varying degrees. It is necessary to sharpen it after adjusting the color level to improve the clarity of printed matter.
In Photoshop software, the sharpening tool is used to improve the sharpness. The method is to select the menu command “Filter/Sharpen /USM Sharpen” and set three variables “Quantity”, “Radius” and “Threshold” in the pop-up dialog box to determine the sharpening amount. It should be noted that the sharpening amount should be adjusted in place at one time, and repeated adjustment will cause the image grain to become thicker.
Different manuscripts have different requirements for clarity, showing hard textures such as architecture, steel and scenery manuscripts, paying attention to detail contrast, and sharpening can be larger; For image manuscripts with smooth surface texture, such as apples and tomatoes, the sharpening amount should not be too large, otherwise it will appear rough, but local water drops can be sharpened separately to make them more transparent and jumping; In the performance of roast chicken, roast duck, etc., the glittering and translucent jade products and cooked noodles, the smooth movement of milk and chocolate, and the smooth and delicate texture of characters’ skin color, the sharpening amount should be smaller. However, when sharpening the original manuscript, it is necessary to enhance the detail contrast of hair, eyes and eyebrows, but it can not affect the smoothness of skin color. The threshold can be set to 5 Left and right, it can not only ensure the clear outline of the manuscript, but also not affect the graininess of the character’s skin color.
IV. Quality inspection It is an important means to ensure successful products to have self-inspection consciousness and habit, reduce quality omissions and improve reproduction effect after the completion of electronic calibration. The quality inspection mainly includes the following contents.
1. the reducibility and artistry of the manuscript The value of product packaging lies in improving the aesthetic feeling of products, thus stimulating consumers’ visual nerves and generating their desire to buy. Excellent printed matter reflects the blending of light and color, and can vividly express the light, distance, perspective and stereoscopic sense of products, but not all manuscripts can meet the quality requirements in practical work. In the electronic calibration, the original color restoration and artistic sublimation should be organically integrated, and the original-based calibration concept should be followed, and the imperfections in the original should be reasonably improved, so that the packaging can better show the basic characteristics of the product and better meet the requirements of customers.
2. Correct the visual defects of digital samples (1) Be careful when placing complementary colors in large red, because the role and visual effect of complementary colors are more sensitive in colorful printing inks.
(2) For 1% ~ 2% of the small dot parts in the manuscript, the digital samples can show elegant color changes, but these subtle color levels are difficult to show in printing. In terms of the level strength of highlights and midtones, the printed samples are usually weaker than the digital samples, so it is necessary to adjust the flood color and level strength of highlights according to the transfer characteristics of printing dots. In the dark tone area, the gray balance of composite color is out of balance, resulting in color deviation. However, due to the high density of dot synthesis, color deviation is not very sensitive in digital samples, but it is much more conspicuous in printed samples, which affects the reproduction effect. Therefore, the inspection of dark tone often needs to be combined with dot data.