Correctly understand and actively implement the newly revised "Quality Requirements and Inspection Methods for Lithographic Prints" (2)

■ China Printing Corporation, Inc. (Continued) 3. Correct application of inspection conditions and scientific evaluation of product quality The new CY/T5 standard has two main components: quality requirements and inspection conditions and methods. Correctly understand the quality requirements will also use the inspection conditions and methods. The contents of the two parts are unified, and on the basis of understanding the quality requirements, the inspection conditions and methods should be reasonably applied to scientifically evaluate the product quality. 1. The connotation of product quality. The ISO terminology of the product is interpreted as "the result of an activity or process" and the quality is interpreted as "the sum of the characteristics of the entity that reflects the ability to satisfy explicit and implicit needs." It explains very principle, but it highly summarizes the essence of product quality through activities to meet and satisfy social requirements. The scope of print is very wide, and the quality of different prints is not exactly the same. The quality requirements for prints based on words or numbers are mainly accuracy, legibility, ink consistency and so on. CY/T5 is an image-based lithographic printing standard. Therefore, hundreds of printing and related industry experts have summarized and determined the tone value, level, overprint, outlets, K value, color, appearance and other indicators as control and evaluation products. Quality indicators. Some people interpret the quality of print as: "The comprehensive effect of various appearance characteristics of printed matter." This comprehensive effect refers to the gradation duplication, the level duplication, the color duplication, the layout clean, and the correct specification of the text map. The evaluation of product quality should be based on the above content. 2. It is necessary to properly equip the conditions for product quality inspection, understand the form of inspection, and learn to use the instruments or tools for inspection. According to the test methods and requirements provided by the standard, inspection and evaluation are performed. The specifications, requirements, principles, and methods suggested in Appendix A (reflection densitometer), Appendix B (calculation method of dot gain value), Appendix C (calculation method of relative contrast value), and Appendix D (measurement control strip) The indicators in the standard are separately controlled, tested and evaluated, and the meaning and requirements of the standard inspection must be correctly understood. On the basis of correct understanding and unity, implement it seriously. 3. Based on a correct understanding of the standard content and testing methods, the inspection and evaluation of product quality should be based on science and technology, and the overall evaluation should be complementary. How to identify the quality of printed products, strictly speaking, there is no unified standard. For customers and product users, they are tested on their own experience and preferences. Generally, there are more subjective components. For designers, publishers, and printing workers, quality inspection personnel and related professionals, the content of standard content should be required. In order to perform comprehensive inspections and evaluations from aspects of design and processing, material conditions, process technology, quality parameters, appearance characteristics, document specifications, and publication requirements, the general requirement is to meet or exceed the various indicators of the standard. To have a good overall effect, to meet the needs of customers, to meet the quality requirements. 4. What indicators should be evaluated for color prints and how to evaluate them are both theoretical and methodological issues. The "Ten Projects for Quality Evaluation of Color Prints" presented in the article "On the Evaluation of the Quality of Color Prints" published in "Print Quality and Standardization," 1999, No. 5, has not been identified after reading. From the tone reproduction to the Murray-Davies formula (Appendix B) and the formula of Yule-Nielsen developed in this formula, and the New Wheel Fortress used in color reproduction (Neugebauer) formulas, etc. do not involve the concept of average. 1 "The field density is the average value of the solid density Di of the four colors yellow, yellow, blue, and black, as the field density value of the evaluation item. That is: D = (Dc + Dm + Dy + Dk) / 4". This formulation is not based on or intended. The actual field density Dy is a violet-blue filter (Kodak 47B); Dm is a green filter (Kodak 58); Dc is measured with a red filter (Kodak 25). Each of Dy, Dm, and Dc absorbs blue, green, and red of the three primary colors of visible light. If the density is sufficient, no reflected light can be superimposed into black. Due to the limitations of lithography, it is not possible to achieve sufficient blackness, so the black version is added for compensation to meet the need for image tone reproduction. The black solid density was measured with a light orange filter (Kodak 106). Black is the result of absorbing all visible light, and the black formed by the superposition of yellow, magenta and cyan is a complementary relationship. The four-color solid density is measured by four different color filters. The four filter's transmission spectral range and light transmission amount are different. Each has its own function and there is no mean value problem; Dy, The average density of Dm, Dc, and Dk four-color solids is less than the superposition of four-color solids, such as Dy 1.0 and Dm 1.4. Dc is 1.5 and Dk is 1.7. The average value is 1.4. The effective density after the actual normal conditions are superposed is 1.8 or so; the four-color solid density is unchanged, and the printing color sequence is changed. If the last printing yellow is changed to the first yellow printing, The effective density of its four-color superposition is also different, but the mathematical average is still the same. Therefore, the concept of the average value of the field density has no theoretical basis, but it is inconsistent with the actual situation, and it cannot be used as a project to evaluate the product quality. 2 "Tune Error": The tone should be understood as a conditional level within a certain brightness range. There are many reasons for the effect of tone copying, but there is no basis for understanding how “level error” is understood. The original interpretation is the characteristic curve drawn by the difference in dot area between the dot ruler of the network and the printed matter. The difference between the two is the “adjustment error”. This explanation is worthy of study in concept, and should be the value of the dot gain, not the “order”. Adjustment error". According to the characteristics of lithographic offset printing, the proper increase in the number of dots when printing is correct. It is possible to enlarge the dot properly to print, and it is wrong not to increase the dots. Therefore, the ideal printing curve is not a straight line but a curve controlled within the allowable range. . Different printability conditions, different printing color sequences, different numbers of screen lines, different dot shapes, and different color version curves are also different. Therefore, the formulation TE=(TEc+TEm+TEy+TEk)/4 is neither meaningful nor valid. (3) "Fineness of the outlets": Objectively speaking, there are many reasons for the occurrence of false outlets. If the performance of the plate is poor, the printing operation is not standardized, the paper and ink properties are lacking, the blanket is aged, the room environment is uncomfortable (low temperature, etc.), the amount of water supplied, the amount of ink supplied, the printing pressure mismatch, and the operation is not proper. The “degree of fidelity” refers only to the “dropout of points and hairlines”. Actually, it also includes the shrinking of the area of ​​outlets, the hollowness of outlets, the shallowing of outlets, the malformation of outlets, and the occurrence of virtual outlets. These are difficult to quantify. The practice of real drop-off points is not common, and many sites are incomplete. At this time, it is feasible to use the dot density control of outlets. No reference was made to this indicator when formulating and revising standards. The purpose is to control the value of the density in the field and the minimum number of outlets. To increase the area and increase the value of outlets. The relative contrast to comprehensively control the full-step duplication curve, indirectly control the network reality, because the actual and false network points directly affect the indicators of image replication. Therefore, the feasibility and accuracy of the method proposed in the article for handling observation scores at 50% of outlets are worth studying. 4 "50% dot gain rate": The standard dot gain value, Appendix B hint is used Murray-Davis formula. The article refers to the difference between the fine mesh density and the coarse mesh density at the 50% dot area of ​​the Lunar test strip. This method has three specific meanings: First, it refers to 6O lines/cm (or refers to 150 lines/inch). If the number of product lines changes, the increase will be converted. (See Table l); Table 1 Increases or decreases in the value of different network cable outlets. ┤ │40 │-1/3 │├─────┼───┤│48 │-1/5 │├─────┼───┤│54 │-1/6 │├── ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────│ 60 60 ┤ 60 60 60 60 60 60 60 60 60 │├─────┼─────┤│100 │+2/3 │├─────┼───┤│120 │+1 │└─────┴───┘二是Refers to the specific structure, the total length of the 50% screen edge length of different shapes is different, the measured integrated density is different, the dot gain value is different; the third is the absolute value at the 50% dot area, the dot gain of other parts is less than 5O% outlet area. Different plates detect the difference in the integrated density of fine and coarse dots, so the dot gain value is also different. It must be controlled during the operation and must meet the requirements of the standard. If three of them are qualified, one color plate is out of standard or the value is not enough, the average value is within the control range, the actual product will cause color cast or lack of color, so the dot gain does not exist DG = (DGc + DGm + DGy + DGk) / The average relationship of 4. 5 "Relative Contrast (K)": It mainly controls the intermediate tone to the dark tone, and it is also an indicator to control the full tone. In theory, if the density of the field, the minimum dot, and the dot gain are well controlled, the K value is also suitable. It should be pointed out that the density of the ground in each edition is very different, so the difference in the K values ​​of each color is also large. Each color has its own role and there is a compensation relationship with each other, but there is no average relationship of K=(Kc+Km+Ky+Kk)/4. For example, when the yellow plate is used in the platemaking process, the removal of the background color, together with its low density in the field, the K value is too small is normal; if the black version uses the short (mostly short tone) tone, the dark tone in the image has The role of background gain, K value is too large is needed, so the standard not only gives the K value of the fine product and the general product is different, but the K value of the yellow product and the product, the green and the black version of the same product are also different. The above content is measured by using the geometrical measurement and control strips of certain known area (mesh, yin and yang, straight lines, broken lines, radiation, etc.), and the calculated data is compared with the data given in the standard. The image quality is controlled indirectly. The quality of the plate is judged through the analysis of the test strip. Under normal conditions, the two are unified. The measurement and control strip is qualified (must be operated under the same conditions), and the product should also be qualified; if the measurement and control If the article is qualified and the product quality is unqualified or unsatisfactory, it must find out the cause and solve it. The measurement and control strip is only the reference material. 6 "Trimity of the third color": I don't know the origin and intention of this formulation. The interpretation from the original text seems to be the problem of gray balance. The grey balance printing term is defined as “the ratio of different dot areas of the yellow, magenta, and blue primary colors to produce neutral gray in printing”. By definition, it is easier to understand the balance of printing grays. It is a measure of the correctness of color screening and color printing, and it is the principle that the entire process of data reproduction, standardization, and standardization are jointly observed and implemented. Due to the limitations of lithographic printing, it is difficult to adjust the gray balance in the middle tone to the dark tone. Therefore, it is compensated by a black tone of a certain tone. The article says "ideal neutral gray density, if the densitometer R, G and B three filter measurements, the density should be equal," I do not know how to explain. Interpretation from the color of the human eye to different wavelengths of visible light is different. "The density of each color plate is measured with different color filters. Can we get equal density? Practice is under the conventional conditions, the density of all colors in the field is yellow 1.O, magenta 1.4, blue 1.5, After the black 1.7 superimposition, a neutral gray can be obtained, and it should be pointed out that factors such as printing suitability and printing color sequence have a great influence on the balance of printing gray, and we must correctly understand and carefully implement the balance of printing gray. With gray rate, color efficiency: these three indicators are used to check the ink properties (primary hue).After the measurement, according to the color cast, the amount of ash in the color separation screen when the corresponding correction to adapt to printing gray Balanced implementation: Different manufacturers of inks, inks of the same manufacturer with different hue, its color shift, ash and color efficiency are certainly not the same, so the stability of the supply of raw materials (ink) is of great significance to improve and stabilize product quality. Refers to the color of a primary color ink containing another primary color ink, the more it contains, the larger the color cast; the gray color refers to the color material of another primary color ink containing two other primary color inks, and the content is similar. Some kind of ink itself The gray component, if a certain color ink contains color materials of the other two primary color inks, and the content is not equal, the ink has both ash and color shift. Under normal circumstances, color shift, with gray Large, the color efficiency is low, otherwise the color efficiency is high.Therefore, it is desirable that the color shift of the ink, the smaller the ash, the better, and the higher the color efficiency, the better.There are causal relationships among the three indicators of a certain primary ink, but The ink of different primary colors does not have the relationship of color shift HE=(HEc+HEm+HEy)/3, G=(Gc+Gm+Gy)/3, color efficiency η=(ηc+ηm+ηy)/3, and it is better not to use three inks (hue). The indicators directly evaluate the quality of printed products.