In general, the subjective and objective inconsistency of the color difference evaluation results of printed colors is expressed in two aspects: one is the color that the human eye can perceive when the same color shifts in different color directions to produce the same color difference value The degree of difference is different; second, when different colors are shifted in the same color direction to produce the same color difference value, the degree of color difference that the human eye can perceive is also different. For the above two points, the experimental method of display simulation can be used for qualitative description. The specific process is: in CIELAB color mode, select 50% CMY three colors and RGB three colors synthesized by them and 50% gray, respectively change the color to make the color change in a certain direction, and observe with human eyes. When the color difference can be distinguished, the size of the change value and the corresponding color chromatic aberration of the same color are shifted in different directions, and the magnitude of the visual impact is different. In general, it has the greatest impact on vision, while changes to similar colors of the color have the smallest impact on vision. This is exactly the case in actual printing. Even if the color difference is small, the darker or lighter printed matter can be easily noticed. This also shows that in the color difference formula, the weight of the influence of the change on the color difference is the largest. Therefore, the evaluation of the shades of colors has high accuracy in visual judgment. The color cast of different colors in the same color direction has different effects on vision. Studying this point is of great significance to the color detection of printed matter. Because in printing, the color deviation of the printed matter is mostly caused by too much or too little ink in a certain color plate, and the color deviation direction is consistent. For example, the yellow version has too much ink, all the colors on the printed product are yellowish, and visually, the areas dominated by magenta ink and cyan ink are biased. From the simulation experiment results of the monitor, it can be concluded that in the CIELAB color mode, the objective color difference value does not really match the visual inspection results. To achieve the unification of the subjective and objective evaluation, it is necessary to analyze the reasons for the inconsistency between the two in order to design Reasonable objective color difference evaluation system finally makes it conform to visual color judgment. In actual operation, there are three main aspects that will cause inconsistency: First, many subjective factors affect the visual evaluation, such as the characteristics of the sample and the observation conditions. Secondly, due to the influence of the design and manufacturing accuracy of the color measurement analysis instrument itself, when the same color measurement instrument performs multiple measurements at the same place on a solid color patch, the color data will not be completely consistent, that is, there is duplication of the color measurement instrument Precision issues. In addition, the color data measured by different color measuring instruments in the same place will not be completely consistent. These instrument errors will affect the accuracy of color difference. MacAdam tolerance ellipse x, y are chromaticity coordinates. The human eye has different wide capacities for different hue colors. The green area has a larger color capacity, followed by the yellow area, and the blue area is the smallest. The lower the brightness of the color, the smaller the tolerance range, so dark samples are not easy to achieve color matching; the lower the chroma of the color, the smaller the tolerance range, so the color of the gray series is not easy to achieve color matching. CIE officially recommended the CIELAB uniform color space and its color difference formula in 1976. Although the CIELAB color space eliminates the difference in the tolerance of different color areas to a certain extent, this space is still very uneven, and its color difference formula does not reflect the color three. The weight of attributes is different, so it has limited value in industrial applications. Generally speaking, the color difference result calculated by the formula is not as good as the actual personal visual judgment of an experienced individual. In addition to applying more scientific design principles to improve the measurement accuracy, the errors caused by CIELAB measuring instruments can also be reduced by using multiple sampling and averaging on the same point during the measurement process and using the same measuring instruments on the same batch of printed products. Small errors, thereby improving the accuracy and repeatability of the measurement. In order to better correct the uniformity of the color space and make the measurement results of the instrument better match the visual evaluation of the color, it is necessary to use more advanced color difference formulas. The above three color difference formulas are corrected to different degrees by introducing different parameter factors. The unevenness of the used color space (CIELAB) is conducive to the unification of subjective and objective evaluation. Considering the complexity of actual printing, by communicating with customers, printing companies can work out different color difference standards for different printing colors. It can be seen that the perfection of the color difference formula plays a vital role in objective evaluation. Melamine Laminated Plywood,Melamine Plywood,Color Melamine Laminated Plywood,Wooden Grain Melamine Laminated Plywood Shandong Yami Import and Export Co., Ltd. , https://www.yamiplywood.com
Third, the non-uniformity of the color space makes the color difference value measured by the instrument not fully reflect the color difference perceived by the vision. The unevenness of the color space can be clearly shown from the experimental results of WDWright and DLMacAdam.