The paper will explain the application of color science in printing from three aspects: the production of printing chromatography, the measurement of printing hue and the matching of spot color ink.
1 Using color science to produce printing chromatography
Throughout the color reproduction process, it has undergone three processes of color analysis, color transfer, and color combination. The correctness of color change control in each process is directly related to the final quality of the printed matter, so a color standard, that is, printing chromatography, is required to regulate various hue in the printing process. Printing chromatography is the use of three primary colors of yellow, magenta, cyan and black, mixed in different proportions or dots, stacked to form a photo album of various colors, for people in design, original copy, ink blending, etc. Check it out.
Four-color chromatography uses yellow, magenta, cyan, and black four-color inks with different dot area percentages (usually only 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% eleven dot grades, or 5% aliquots of dot grade) overlay overlays, arranged in a certain order, it has the same process for electronic color separation, proofing and printing Important reference and guidance. The spot color in printing is a color ink that has been mixed, and the color is not directly related to Y, M, C, and K. Therefore, a set of standard primary color inks is first defined, and various kinds of mixing colors are produced according to different mixing ratios. The color chromaticity sample, each color sample is marked with a scalar indicating the mixing ratio of the primary colors, so that people can use the three primary color inks to blend the color colors of various colors. This is the spot color chromatography.
At present, Pantone color matching chromatography of American PANTONE is widely used in the world. However, printing chromatography uses color to indicate color. Its production is usually affected by many factors such as ink, paper, printing process and equipment. Therefore, the printing unit should make its own special according to the raw materials, production process and equipment conditions used by the factory. Printed chromatography.
2 Using color to measure color and color difference
The color measurement in color printing can be roughly divided into three types: contrast visual method, density measurement method and color measurement method.
The color measurement is measured by the contrast visual method in the printing process, mainly by an experienced operator who evaluates the color of the original, the signal strip, and the printed sheet by a comparison visual method with reference to the standard color ratio. Due to the influence of the observer's own physiological and psychological factors, the accuracy of the comparison visual method is relatively poor. However, because it does not need to be equipped with fine measuring instruments, it is widely used in general copying work.
Densitometry is a method of measuring the tone and color of a color using optical density values. In the color printing process, the density value can well reflect the proportional relationship and superposition performance of the three primary color inks, and the detection equipment is simple, so it is widely used. However, the optical density is used as the monitoring and measuring method of the printing process. The size of each monochromatic ink can only be obtained from the control strip, and the information of the color error cannot be directly obtained from the image, so that it is difficult to communicate with the printing customer, which is inconvenient. Density measurement is precisely controlled, so density measurement is just an indirect method of color measurement.
The chromaticity measurement method is based on the principle of colorimetry, which uses the color of the important part of the printed image as a monitoring point, directly measures the tristimulus value of the color, and acquires the color measurement method of the color chromaticity information. The method can accurately express the color difference between the standard proof and the sample to be tested and the required proximity, without additional check or control strip. However, it has not been promoted and popularized at present, mainly because the instrument is expensive and has high color theory requirements for users.
In the color printing copy work, not only to understand the three attributes of the color, but also to understand the difference between the colors, in order to compare and distinguish the color, which is the color difference. The unit of color difference is NBS, which is an abbreviation of the US National Bureau of Standards. At present, the color measurement standard commonly used in the world is the CIE1976Lab uniform color space, which was proposed by the Canadian Weizesky at the 18th CIE Conference in 1975. Where L is the psychological brightness, a and b are the psychological chromaticity, and the color difference is represented by △E. When a is positive, it means reddish, when it is negative, it means greenish; when b is positive, when b is positive, it means Yellowish, when it is negative, it means bluish; when L is positive, it means light color, otherwise it is darker. The color difference ΔE is generally less than 3, and the chromatic aberration is not very large, but it is also affected by the deep, light color and the printing material.
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