Brief Analysis on Color Correction of Gravure Printing (Part One)
Processing of color cast of original manuscript At present, there are various color cast in many original drawings. Therefore, the correction of color cast is an important content in the color matching industry, and the following essentials should be mastered:
(1) color cast positioning:
Firstly, analyze whether the color of the original (including light and disk) is color cast. Typical color cast is mainly manifested in neutral gray and color part of impression. When positioning color cast, first, it depends on eyes; second, it uses suction point value and gray balance value of our company to determine whether color cast. Methods of visual recognition of color cast; (1) see if the black, white and gray in the image are color cast, because people are most impressed, sensitive and easy to identify whether they are color cast, as long as the black, white and gray in the picture are correct. ? Explain that the original color tone is correct.
② Look at the colors of the most familiar parts, such as the skin color of characters, whether they conform to the characteristics of children’s skin color, young women’s skin color, actors’ skin color, whether they conform to the skin color people expect psychologically, and whether there are defects such as yellow, red and gray.
① See if the important impression colors in the image, such as big red, green, orange, tomato, banana, red date, walnut, strawberry, etc., conform to the real color of the objective objects in the impression, conform to the color provided by the customer, and have color bias.
(2) What color to choose?
(1) with black, white, gray as a benchmark, see what color black, white, gray, blue, red or purple, etc.
② Based on the skin color of the characters, combined with the skin color expected by people’s psychology, we can see whether it is yellow, red, gray or dark.
(3) according to the real color of objective objects, according to the requirements of customers, see what colors are important for various subjects. For example, big red is magenta or orange red, and green is bluish green or yellowish green or dark; For example, orange, orange is partial to yellow and lacks magenta, or partial to magenta and lacks yellow, or partial to gray, etc., only to accurately determine whether or not the color is partial and what color is partial? To correct the deviation? ?
(3) Correction method:
① Correction of white tone: firstly, if there is hierarchical texture in the white tone, use the highlight end tool of hierarchical curve to correct it according to the ratio of neutral white dot value; secondly, if there is no hierarchy in the white tone, you can correct it by selecting the white block tool in color correction.
② Moderate gray correction: Using the middle tool of hierarchical curve to correct the deviation according to the neutral gray dot value, two situations should be paid attention to: First, observe whether the dot value of the color-biased part is close to the original density value, if the dot value of the color-biased part is deeper than the original density, the biased color plate can be reduced, if the gray is colder, the C version can be reduced, which not only achieves gray balance, but also makes gray reduction lighter. Second, if the dot value of the color cast part is lighter than that of the original, and needs to be deepened, the opposite color can be deepened, for example, the Y version can be deepened, which not only achieves gray balance, but also deepens gray.
③ Black tone correction: First, there are layers in dark tone and black, and the dark tone segment tool of hierarchical curve should be used to correct the deviation according to the ratio of neutral black dot value; Second, if there is no hierarchy in dark tone and black tone, the black tool in color correction can be used to correct the deviation.
④ color part correction: color correction: y, m, c, r, g and b hue of the color correction tool selected by Photoshop software should be used for correction, and the correction should be based on the saturation of the color, such as green is rather turquoise, not bright, whether to add yellow or reduce cyan. If the dot value of yellow color has reached about 95%, and cyan is 90%, then cyan should be reduced to 80%. If yellow is 85% and cyan is 80%, the yellow should be deepened to 95%.
Note: When selecting the color correction tool to correct deviation, it is extremely sensitive to the color with large saturation, but slow to the gray color. If the amount of color correction is large, it must be checked out separately for adjustment, otherwise it will affect the color change of the same color system.
9. How to deal with the black tone? At present, how to make good use of the black plate and deal with it is a subject to improve the quality of gravure printing products. The author sees that many plate-making companies have appeared many junk products and caused many difficulties in printing due to their failure to deal with the black plate. The author has studied in the long-term production practice, summed up the methods and essentials of dealing with black plate, and immediately improved the product quality in some plate-making companies, and made the printing good, which was praised by customers.
(1) The original manuscript with color as the main color should adopt the process with the three primary colors as the main color and the black version as the short tone skeleton, and the black version only plays the role of spiritual outline.
(2) Some manuscripts with bright and medium tones and few gray and dark tones do not have black marks such as black characters on the packaging bags, so they simply do not use black plates and adopt the process of making plates in three primary colors. If it is marked, the color picture can be made in three primary colors, while the black version is specially used for black characters, thus solving the printing contradiction between the black in the dark part of the image and the black characters outside the picture during printing. In printing, both the blackness and blackness can be achieved, and the dark part of the color picture will not appear in a lump of blackness, thus achieving the best of both worlds.
The light and dark levels in color are dealt with, and complementary colors are used instead of black plates.
For example, (a) the shadow and neck part of a character’s face are equipped with 10%-15% small black screen dots in normal four colors, and the printed ones appear coarse particles. The author removed the black screen and copied 10%-15% black screen dot values onto the green screen, so that the printed face shadow and neck skin color appear smooth and delicate, and the quality is obviously improved; (b) In the bright tone level of green, the complementary crystal color is used instead of black, and the effect is excellent. For example, in the bright middle part of green, the original dot value is 23% for M-color plate and 20% for K-color plate. Instead, 20% of K-color plate is removed, and the calculation is copied to M-color plate, that is, M-color plate is 43%, so that green is bright, rich in layers, and delicate and not rough.
(3) Some black-based manuscripts, such as “Black Sesame Paste” packaging bags, adopt the long-order black version (GCR) process, which can not only make full use of the black version to express the hierarchical texture of “Black Sesame Paste”, but also ensure that the black color is stable and not biased during printing.
The author made a series of more than 10 kinds of “black sesame paste” packaging products in a plate-making company, using GCR long-order black adjustment process.
The setting value is: (a) the highlight part of the required level, k7%? 8%, C4%, M3%, Y3% (C, M, Y can’t be transferred when printing, in fact, there are only small dots in black version, so C, M, Y are put at 4%, 3%, 3%, mainly to make the high tone level continue transition); (b) The dark part, K 90%, local deepest part 95%, C 75%, M 72%, Y 72%, has excellent printing effect, and customers are quite satisfied.
(4) Because the black ink particles are coarse, and the electric engraving uses high screen lines in order to ensure the accuracy of small black characters, the screen dot is enlarged more when printing, which is almost 80% or 85% for medium and low speed printing machines. Therefore, there are two essentials to deal with the black version of the dark part of the image: first, the black version level of the dark part should be consciously opened; Second, the amount of black can’t be set deep, and the best is 70%, so that it can be distanced from the black characters outside the picture, thus ensuring that the black characters can be printed deep when printing, while the dark tone of the image can keep the level.
(5) Pay attention to the difference between shadow black and black objects. Shadow black, that is, sub-black parts of objects cannot be deep. To maintain the level, the black version of black objects can be deeper, and local black can reach about 80% to make black objects deep. Nowadays, many operators often treat the shadow black of an object as a black object, and set the black version very deep, thus causing the printed product to be completely dark.