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The use of standard light sources in color management (Part 1)

the reason why the world we live in looks like a colorful world is because of the existence of light and visual nerve. The photoreceptors in our eyes sense different wavelengths of light from the outside world, which makes our world look colorful and colorful. People always like beautiful things. They hope that beautiful colors can be kept around or shared with more people. Therefore, they began to copy colors, and then various color related industries such as painting, photography, printing, spray painting and so on. However, color is an elusive thing, which is not easy to grasp. It is not easy for the global EPS output of color to reach 6million tons per year. Therefore, people have introduced the concept of color management system in the printing field. In order to get the printing effect as consistent as possible with the original, color management has been introduced into every production process: from the input of the original - electrical scanning or digital photography, to the image on the display, to the traditional or digital proofing of the sample, to the comparison between the finished printing product and the sample, scientific color management has been added to every link, so as to maximize the accuracy of color reproduction. In China, color management can be said to be a new concept, but it is rapidly being accepted and applied by domestic color related industries, especially the printing industry. More and more enterprises engaged in color management solutions have entered this market, and more and more enterprises have applied color management systems to their own production processes

so what is color management? Now people say color management generally refers to the management of color space (scanners, computer screens, printers, printers, etc.) transfer. At the same time, it should also include the management of color consistency, repeatability, or stability. For the current printing industry, color management is very important, because many of the pre production of printing business is completed by advertising companies, and many businesses are not always printed in one enterprise, and there is also a need for communication between printing plants. For such an open system, it needs more coordination, a lot of time and manpower for color modification, To eliminate the color deviation caused by different environments. Color management has more meanings. If every enterprise has a perfect color management application, this process can be greatly simplified. Printing plants can clearly predict and reproduce the color effect of advertising design, and it is easy to achieve the same print color among printing plants. Therefore, the real role of color management is that it is a bridge for color communication, and everyone can benefit from it

the color management system is not a simple software system, which is the misunderstanding of many people about color management. The color management system should be a system in which hardware and software cooperate with each other. It should include the following elements:

first of all, the hardware system. Computers, monitors, scanners or digital cameras, printers, printers and color measuring instruments are all hardware elements for color management. How to use instruments and software to coordinate and manage the transformation of colors in these spaces is one of our ultimate goals for color management

however, the color characteristics of each device are different, and even the characteristics of two machines of the same model are different. Therefore, the second important element for scientific color management is the device profile. This file is to measure the color samples of the printing equipment through the spectrophotometer, and then calculate in the professional software to generate the ICC profile file. It can accurately describe the color characteristics of the printing equipment and determine the quality of the printing color management effect. The accurate ICC profile depends on the accuracy of the measurement system used, as well as the algorithm and control parameters that generate the ICC profile software. Therefore, the accurate feature file of each device is one of the indispensable elements of color management

moreover, it is the reference profile of the simulation object. Color management is an attempt to use a limited number of devices to make color more predictable. It uses a device independent color characteristic description file to connect the space of each device and the standard color characteristic description file for comparison when converting colors between devices. The color characteristic description file is characterized by the feasibility of color reproduction of devices, and the color management module (CMM) performs color conversion, By using the color characteristic description file for each device and color management module, it can provide a wide range of characteristics, and reduce the time and cost of color reproduction

the last point, which is often overlooked, is to observe the color environment, that is, the composite material company and strength Institute of the light source ring United aviation industry. The final judge of the results of color management is human eyes. No matter how the equipment is adjusted, the color image and difference, accuracy and inaccuracy are determined by the observer through his own eyes, because a string of values can only give people an abstract color concept. As we usually say, seeing is believing, people always believe in their own eyes. But the eyes will deceive you, or the light will deceive you. Sometimes different colors will make you look the same under the same light source, but the same color will look different under different light sources. Therefore, in color management, we must create a good, stable environment for observing color, which can see the true color as much as possible. Of course, the most ideal environment is the environment under the natural light on a sunny morning, which is the best observation environment, but it is also a very difficult environment for practical operation. Because we always carry out color management indoors, we need to use an artificial light source to create an environment that can imitate the ideal natural light as much as possible to observe color. This artificial light source is the standard light source. Only in such an environment can we correctly carry out color management and accurately evaluate the results of color management

why do colors sometimes look the same and sometimes different? Why does color management need standard light sources to create an observation environment while other light sources can't? Let's find out why

as mentioned above, the final judgment of color management should be observed through our eyes. Let's first understand why our eyes see different colors? Let's first understand why our eyes can see different colors. Color is the response of visual nerve to light. It is a kind of visual nerve stimulation. Without visual nerve or light, there will be no color. Note: light is not equal to color. The wavelength of light that can be seen by people is generally between 380nm and 780nm. The following are the wavelengths of visible light

light color wavelength λ (nm) stands for wavelength

red 780 ~ 630 700

orange 630 ~ 600 620

yellow 600 ~ 570 580

green 570 ~ 500 550

cyan 500 ~ 470 500

blue 470 ~ 420 470

violet 420 ~ 380 420

from the perspective of application, the band from 600nm to 780nm is red light (R), yellow light (y) from 570nm to 600nm, 500nm to 570nm is green light (g), 470nm to 500nm is cyan light (c), and 380nm to 470nm is blue light (b). We can find that R, that is, the wavelength spacing of red light is 180nm, that of G is 70nm, and that of B is 90nm, which accounts for a larger proportion in the visible spectrum than that of Y and C, respectively. This constitutes what we call RGB color light. The generation of white light is the complete transmission or reflection of all light. We can see color because there are three cone-shaped cells in the optic membrane of our eyeballs, which are responsible for receiving color light ργβ And rod like cells responsible for sensing light and dark. Among them, the cone cells are responsible for the sense of red light ρ, Responsible green light is γ Pyramidal cells, responsible for sensing blue light β Pyramidal cells, together with rod-shaped cells, form the main light receptor of our eyes. Then it is transmitted to the brain through nerves, forming our sense of color. So we can see objects of different colors because light shines on the colored objects. The colored objects absorb some light waves and reflect some light waves. The reflected light acts on our eyes, so the world looks colorful

in other words, color is the brain's perception of the R, G and B stimulus values formed by light acting on the cells on the visual membrane of the eye. Its 2600 ⑵ 900 Ma products have begun to use high nickel 811 materials. That is to say, if the calculated results of the three stimulus values x, y and Z of R, G and B are equal, even if the spectral distributions of the two color objects are different, we feel that their colors are still the same

although the spectral curves of color object 1 and color object 2 are different, the XYZ values calculated by the two under illuminator C are equal, that is, the three stimulus values of color object 1 and color object 2 on the eye membrane under illuminator C are equal, so the brain feels that they are the same color. We call this the illuminant conditional isochromatic phenomenon, or the same color but different color phenomenon. If we replace illuminator C with illuminator a

under illuminant C, the XYZ values calculated by color object 1 and color object 2 are different, that is, the three stimulus values for the visual membrane of the eye are different, so our brain feels that these are two different colors. This is why different colors appear to look the same under the same light source. Similarly, if the spectrum of a color object is the same, it is possible to produce two different tristimulus values under the irradiation of two different light sources, so the color will look different

from this, we can see that the illuminant is one of the important factors affecting the color. In the process of our color management, if there is no standard illuminant or light source that can play a role in communication, the results of our color management will be greatly reduced. This is also the reason why the standard light source of D50 or D65 should be used as the basis for color communication in the printing field

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