As we all know, when we talk about color management, we will think of the conversion relationship between two characteristic files, and these two characteristic files are the characteristic file of the source device and the characteristic file of the destination device. The characteristic file of the source device contains exactly what kind of color information is in the file, and the characteristic file of the device contains what kind of color information can be copied on the target device. And whether the color information restored from the device space is the desired color information in the source file, it needs a heavy-weight color module to control it, which is the CMM (color management module), also known as the color engine. CMM is the most basic and important part of the color management system. It provides the color management system with a color conversion method from the source device color space to the PCS, and then from the PCS to any target device space. This conversion method, In fact, it is achieved by modifying the color information sent to the target device space RGB or CMYK value. As for how to modify, through what modification, how to define the modified value, this is only understood by the psychology of the various manufacturers of CMM, which is why there are so many CMM manufacturers (adobe, agfa, apple, heidelberg, koda, x-rite, etc.), the reason for the deviation of the color converted by the CMM of different manufacturers. There are two main factors that affect it: interpolation algorithm and white point adaptation. The two aspects are discussed below. 1. Interpolation algorithm. The interpolation algorithm is to use the function values ​​of the function at several points in a certain interval to make an appropriate specific function, take the known values ​​at these points, and use the value of this specific function at other points of the interval as the approximate value of the function; CMM interpolation The algorithm is also based on this algorithm principle. Simply put, it is based on a specific set of algorithms to select representative color matching values ​​on RGB or CMYK nodes to define, so as to achieve the purpose of simulating the entire color space . Example: Under normal circumstances, each of the three channels of the RGB device contains 256 discrete values. In this way, the RGB color space contains a total of 16.7 million RGB color values ​​of the PCS definition. If each PCS definition Using three values, each value is calculated by one byte, then the information amount of such an RGB characteristic file will be huge, and then embed this huge amount of information into the RGB picture, or one of multiple such pictures In the large version of the file, the space occupied by the file will be unbearable. If this is the case, who would use such an intangible thing? Based on such data volume and transmission speed considerations, when the "cost-effectiveness" is sufficiently high, the CMM difference algorithm came into being. Ideally, we should do interpolation calculations in the CIE LAB color space and use LAB as the PCS. At this time, for CMM, the only thing it needs to do is to obtain the corresponding LAB value in the input characteristic file. Find the closest PCS value in the device characteristics file, and find the corresponding output value. If reasoning is based on this concept, CMM is not very useful, and the actual situation is indeed the case. If it is carried out in this way, it will not get an ideal result in practical application, because according to this algorithm The result of LAB is not as uniform as we think, and there will be an unexpected result, such as the actual value does not really correspond to the desired value. Based on this consideration, different manufacturers will use different difference algorithms. The difference algorithm of different manufacturers is mainly reflected in the selection of nodes and the optimization of calculation, which can be generally divided into three categories: A. The first-class manufacturers use some mathematical formulas and clever algorithms to compensate for the lack of LAB color space and correct its inaccuracy. It uses a special method to achieve the uniformity and smoothness of the LAB color space, to "deceive" the eyes of color users, but the actual effect is not as perfect as it looks. B. The second type of manufacturer does not use LAB color space, but converts the color to other color space for interpolation, so that the characteristic file looks more perfect and perfect. C. The third type of manufacturer is to use any special color space in addition to either LAB or XYZ when creating a characteristic file, so as to ensure uniform and smooth color space. This approach first violates the principle that the feature file is open and interchangeable, and the most important thing is that its actual effect is not as perfect as it looks, although it can indeed compensate for the uneven reality produced by interpolation of some feature files. . Different manufacturers have different interpolation algorithms, which also leads to different reasons when using CMMs of different manufacturers. For example, for the processing of some highly saturated colors, the results of different CMMs will be It varies greatly, and even worse, it will convert the blue sky into a purple one. 2. White point adaptation. The ability of the eye to adapt to changes in white field color, and white field is the brightest white color and its light intensity that the device can reproduce. Relative to our focus on the density of black dots rather than color, for white dots, we are more concerned about its color, which is why we may compress some of the colors for the white field when doing monitor calibration The reason for its brightness. When the human eye is "processing" white, it will always automatically adapt to it, and then judge and adapt to other color feelings based on this white. It is precisely because of this, the first thing we do when we do color conversion is Convert the white point of the source device color space to the white point of the target color space. But sometimes when we perform this conversion, we find that the white point of the source device is not the white we want when it is on the target device, but it may be that the relevant color information appears on different color channels. When I saw another color management software, I found that this kind of situation did not happen again. This is because the CMMs of different manufacturers deal with white points differently and produce different results (this has nothing to do with the four mapping methods). The difference in the processing method of the white point directly results in that the white point of the characteristic file is not on the same main axis, which causes the entire neutral gray to be biased to a certain hue, and all the colors produced by it will be biased. [next] As shown in the figure below, we use the ICC --- G7HD-2-340K95 generated by the 210 color targets included in the Print open software. icm For the same 210 color targets, we use ICC ---- ProfileMakerCGATS-edit generated by profilemaker. icm It is clear from the above figure that when different manufacturers perform CMM, the algorithm of the white point is different, and the difference algorithm of the generated characteristic file is also different, which leads to such a big difference between the two ICCs. In our color conversion process, CMM is everywhere, PC and Apple system, all application software related to color. So how to use and how to choose is where we feel we have no way to start. Although we will have a lot of choices for color management software, although there are related CMM modules in color-related application software, although ADOBE has now opened its own CMM module for free, in actual use, we should try our best to Only uses one CMM conversion module, the purpose of this is: 1. Avoid using CMMs of different manufacturers for multiple conversions, which will produce unexpected results, and may cause color inconsistencies due to inconsistent conversion methods of different manufacturers; 2. Even if there is a problem, we can have enough ways to find the cause of the problem, rather than because we have used multiple CMMs and it is impossible to start; 3. Even if the same CMM is used in different operating systems or application software, the deviation problem after color conversion will be generated as little as possible; 4. More importantly, after using only one CMM, we can have enough experience and actual data to judge the advantages and disadvantages of this CMM. In the world of colorful colors, CMM is destined to be an obscure but untiring "underground worker". What it brings us is to ensure the accuracy of color conversion between different systems and different devices. At the same time, it is It is the "criminal culprit" that makes colors intricate. We can't control its destiny (only manufacturers can control its power of life and death), but we have the right to choose to use it to master its internal laws, so that it can truly play the "positive role" of color conversion. Wooden Pepper Grinder,Rubber Wood Pepper Mill,Rubber Wood Black Pepper Mill,Rubber Wooden Manual Pepper Mill YangDong Q-Bamboo Houseware Co.,Limited , https://www.q-bamboo.com
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Factors affecting CMM (Color Management Module)