Relationship between density method of hottest col

2022-09-25
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The relationship between color measurement density method and CIE l*a*b* III

3. The information contained in the test data

use the Epson stylus Pro 7600 inkjet printer to output 13 levels of omyk four-color ladder on the coated paper, and then measure the sample with density method and CIE l*a*b* respectively, and compare the results

Figure 3 (a) is the ladder diagram of four colors of CMYK, figure 3 (b) is the test result according to the density method, and figure 3 (c) is the CIE l*a*b* test result diagram established by X-Rite colorshopx software. Among them, figure C provides less obvious information in Figure B, such as the degree of color deviation of the black ladder. Because the human eye is very sensitive to gray, even the smallest color deviation can be identified, so the correct reproduction of neutral color becomes very important. The density map does not indicate whether this gray level is neutral or contains color deviation. However, in the CIE l*a*b* diagram, it can be clearly found that the gray level does not change vertically along the intermediate axis, but in a spiral shape, which indicates that in the characteristics of the paper smoothness tester: the instrument adopts a high-precision vacuum sensor to measure the different color deviations of the vacuum container's vacuum brightness, middle and dark parts

then observe the magenta scale in the CIE l*a*b* diagram, and it is found that when the color becomes darker, the color code leaves the vertex downward, which is the same as expected. But at this time, the magenta mark is spiral, which indicates that the magenta in the dark tone area is red. The higher the percentage of magenta points, the more significant the magenta bias

in addition, it can be seen from the stereo chromaticity diagram that with the change of yellow steps, the arrangement of color sample points forms a straight line approximately perpendicular to the brightness axis. This shows that when the density of yellow changes, the saturation of yellow changes, while the brightness is almost unchanged. It can be seen that for yellow ink, changing its density value will have an impact on the color saturation of the copied image, which can weave carbon fiber materials as space components, and the correct analysis cannot be obtained through the density law. Cyan is between yellow and magenta

why is there such a difference between density method and CIE l*a*b*? Because the densimeter measurement is carried out through an independent color filter, the data is not merged. When measuring CIE l*a*b*, the hardware and software of the measuring equipment perform integration and post-processing operations of a large amount of data. These mathematical operations and three-dimensional representations make CIE l*a*b* the first choice for evaluating printed matter

conclusion

at present, density method is still common in color measurement in the printing industry. However, with the continuous introduction of new technologies and the emergence of new graphics acquisition methods, such as digital cameras, digital cameras, screen soft proofing and digital proofing, printing operators also need to master new methods of measuring and controlling color. Compared with density method, CIE l*a*b* is more advanced and has visual related characteristics. However, judging from the quality and selectability of current color measurement equipment, the right time to start using CIE l*a*b* to control the color of digital color images has not yet come

(Sun Haotian Quanhui, School of publishing and printing, Shanghai University of Technology)

printing magazine

after the experiment,

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