Research on Application of Multispectral Color Copying Technology

There are many theories for the evaluation of color reproduction. Among them, the famous British color expert Hunt, through the comprehensive analysis of various factors, the color reproduction is divided into six types: spectral color reproduction, color reproduction, correct color reproduction, equivalent color reproduction, corresponding color reproduction and Like color reproduction.

Although the conventional color copying method successfully realizes two methods of color reproduction and correct color reproduction, it is unable to realize the unconditional reproduction of color, that is, spectral color reproduction, because of the inherent characteristics of the metamerism. The multi-spectral color reproduction technique uses a multi-primary color imaging method to increase the color gamut by increasing the degree of freedom of color reproduction. The spectral matching reproduction method eliminates the problem of metamerism, thus achieving unconditional matching of colors. This technology is of great significance to the development of high-fidelity printing technology, and will certainly become the direction of future printing industry development.

First, the defects of the traditional four-color printing

Traditional printing uses CMYK four primary colors for color reproduction. Due to its limitations, four-color inks cannot cover all spectral information of the original color. In fact, traditional four-color printing is based on the principle of metamerism to achieve color reproduction. The principle of metamerism refers to the fact that in the printing and copying, as long as the color of the printed document is the same as the color of the original, even if the spectral composition of the two is different, it can be copied and approved as the correct color. This method greatly reduces the difficulty of color reproduction, and in most cases can achieve the correct reproduction of colors, thus constituting the basis for the realization of traditional printing methods. However, when the illumination source and the observer change greatly, the copying effect tends to show a large deviation. This issue is also an important source of quality disputes in the traditional printing industry. In addition, the color that can be reproduced by the four-color printing is only about half of the visible spectrum color gamut, and the effect of copying a large color image with a large dynamic range is often unsatisfactory. Under the current state of the art, even if people perform precise color management and color gamut matching during copying, the problems of metamerism and gamut too small cannot be solved fundamentally.

The traditional printing method focuses on matching the density of the original with the printed color density. However, this matching approach focuses too much on the discussion of the amount of ink and ignores the problem of matching the color and brightness of the copied color. In fact, due to the limitations of the color gamut of four-color printing, it is often in a paradoxical position when regulating color components and neutral gray components. It is inevitable to increase the color component ink to increase saturation. The neutral gray component is increased to reduce brightness. In other words, four-color printing tends to emphasize the reproduction of saturation excessively, and it is necessary to use the method of sacrificing the brightness.

Due to the above-mentioned defects of traditional copying, the effect of copying is often unsatisfactory, mainly due to the heavy color of the image, poor stereoscopic effect, more serious level loss, and different levels of color distortion.

Second, the advantages of multi-spectral color reproduction technology

The multi-spectral color reproduction technology achieves color reproduction by acquiring, analyzing, and processing multi-spectral data. This technology uses spectrum matching as a color reproduction standard, and enlarges the reproduction color gamut by increasing the degree of freedom of color superposition. Due to the uniqueness of the spectral reflection curve, the reproduction effect can be kept stable regardless of changes in the light source and observation conditions. In addition, the sampling of multiple bands of spectral reflectance can record color characteristics as detailed as possible, effectively solving the problem of too low data accuracy in the traditional mode.

In the field of color reproduction, the principle of color reproduction of digital devices such as monitors, printers, and scanners is very different from the formation mechanism of human eyes. Due to its own limitations, the traditional four-color printing model cannot solve the problem of color deviation fundamentally even with the aid of a color management system. The multi-spectral replication technology greatly improves the integrity of data acquisition by increasing the number of sampling channels, thereby achieving high-quality color reproduction. In view of the above advantages, this technology has been successfully used in the field of copying and preservation of valuable art works as well as online shopping. At the same time, this technology also lays a solid foundation for future high-fidelity printing and cross-media publishing.

Third, multi-spectrum replication technology process

Multi-spectral color reproduction technology describes color information as spectral data by describing color spectral reflectance or transmittance. The specific process flow can be divided into the following steps:

1. Data acquisition

Use multispectral cameras with multicolor filters to capture multispectral image data of originals or objects. Typically, the acquisition system consists of a multispectral light source, a color filter, and a multispectral camera. Compared to the traditional three-color image acquisition method, this system has the following advantages:

The light source has a short start-up process, a wide spectrum, and a high radiation efficiency; the color filter has strong transmissivity and is free from background light interference; it can acquire high-resolution data, a variety of data support modes, and high imaging contrast.

After obtaining the spectral data, it needs to be analyzed and processed to achieve high-precision spectral reconstruction. The matrix representation of the mathematical model for multispectral data acquisition is now described as follows:

Let the spectral power distribution of the multispectral light source be S, and the spectral emissivity of the object be r, r = [r1, r2, ... rn]T, where n denotes the number of sampling wavelengths, and T denotes the transfer rank operation of the matrix. In a multi-spectral camera, the spectral transmission characteristics of the m color filters can be represented by the matrix F, and the spectral sensitivity of the detector is represented by the matrix D.

Integrating the above matrix, the colorimetric integral formula can be obtained, and the color value of the collected color is t=(DF)TSr. Subsequently, the color tristimulus values ​​XYZ and CIELAB can be obtained through corresponding linear and nonlinear transformations. Coordinates and other color values.

In addition to the methods described above, principal component analysis (PCA) can also be used to select the optimal filter design and achieve more accurate spectral reconstruction. This method is often used in the mutual conversion between the integral density and the analytical density in the photographic technique, and it is also commonly used in the establishment of a scanner's high-precision equipment property file.

2. Prediction of the original colorant and selection of the best ink color

After the multispectral data acquisition is completed, data analysis needs to be performed. Through the prediction of the spectral distribution of the collected color, the best ink selection of the color reproduction is determined, and the effect of the same-color different-spectrum phenomenon on the color matching is maximally eliminated. In order to achieve the best match between the copy color and the original color, it must be ensured that the spectral distribution curve of the color copy is approximated to the spectral distribution of the original color as much as possible. In actual operation, the principal component analysis method is usually used to analyze and process the spectral data, and then the actual possible optimal color material selection is predicted through the limited rotation transformation. Finally, the best ink selection scheme is finalized by comparing the predicted combination of colorants with the ink combination in the database.

3. The establishment of ink overprint model and spectral prediction

There are many theories about the establishment of the halftone model in color reproduction. In general, people use the Kubelka-Munk theory to calculate the primary color reflectance of the modified Negeber model by Yur-Nelson. Among them, the modified Negeber model (YNSN model) is the most commonly used reflectivity prediction model, which explains the correspondence between the reflectance of halftone printing color spectrum and the dot area ratio at each wavelength. The optical dot expansion problem is taken into account and its specific formula is:

λ=1...8

Among them, Rprint, λ represents the reflectivity of the printed color, n is the Yule Nielsen factor. Rp,λ is the spectral reflectance of the negboer p-type primary color, and αp is the dot area ratio of the primary color.

4. Color separation and printing based on spectral data

The color separation technology based on multi-spectral data is the core of the multi-spectral color reproduction technology, and is usually implemented by inverse transformation of the YNSN model. When using the YNSN equation to obtain the spectral value of the ink dot, an appropriate non-linearization optimization iteration method should be used to determine the color separation settings for each primary color ink. The color look-up table of this separation technology is based on the same principle as the four colors. The difference is that the hue interval of the color space needs to be rationally divided so that the ink color matching input color can maintain the minimal degree of homochromatic spectrum, and the matching is improved. Accuracy. Since the separation effect can maximize the approximation of the original, this technique is often used for high-fidelity printing.

After color separation is completed, multi-color printers or printers can be used for multi-primary printing. Compared to traditional printing methods, multi-spectral replication technology has a larger gamut space and can reproduce more vivid real colors. In addition, the sense of layering of its prints is more realistic and the effect of visual change is closer to the original spectrum.

Fourth, the current status of multi-spectral color reproduction technology and related institutions

1. Research content of multispectral replication technology

According to different stages of color processing, multi-spectral color reproduction can be roughly divided into three directions: data acquisition, data processing, and color output. Each direction can be subdivided into several sub-directions:

Data acquisition: device characterization methods, filter design, multispectral camera tuning, and data recording.

Data processing: color space conversion, color gamut matching, spectral data encoding and decoding, etc.

Data output: establishment of a comparison table, study of color separation algorithms, ink selection, etc.

2. Related institutions

At present, many international organizations, laboratories, and research institutes around the world are working on multispectral color reproduction technology. Well-known universities include the Munsell Color Science Laboratory at Rochester Institute of Technology, North Carolina State University, University of Leeds, UK, and Chiba University in Japan. In addition, IS&T of the Society for Imaging Science and Technology, SPIE of the International Society of Optical Engineers, and the IEEE of the Institute of Electrical and Electronics Engineers of the United States have also made significant contributions to this study.

At home, universities such as Wuhan University, Beijing Institute of Technology and Jiangnan University have also conducted research in different directions on this topic.

3. Problems at the current stage of research

Although the advantages of multi-spectral color reproduction technology in spectrum matching are undoubted, the perfection and popularization of this technology still require the joint efforts of the printing industry and researchers compared to the mature traditional printing technology. At this stage, the high cost of this technology and the complicated operation techniques make most people discourage it. In addition, this technology requires very high precision in data sampling and processing. According to the relevant research done by the Institute of Multimedia Information Technology of the Italian National Research Institute, the effect of multi-spectral color reproduction is achieved when spectral data cannot meet the required accuracy. Very unsatisfactory. That is to say, although spectral matching is the most advanced color matching, there is no doubt that the degree of spectral matching is not directly related to the difference in color difference and the difference in human vision. Obviously, although its advantages are obvious in principle, its actual implementation is actually more difficult.

V. Conclusion

Traditional four-color printing has the fundamental defect of this metamerism, and its color matching can only be maintained under certain conditions. For this reason, more and more people are focusing on multispectral color reproduction techniques that can realize unconditional color reproduction. Although this technology is still at the initial stage of development, its advantages of accurate color reproduction will certainly become the focus of future industry research and lay a solid foundation for high-fidelity printing.

Shoe cabinets keep footwear neat, tidy and out of sight. Fold-down cabinet doors open to reveal organized shoe racks and close to create a polished appearance.Save time to search for shoes by organizing your collection in one dedicated storage space. The easy track shoe tower keeps up to 15 pairs of shoes and boots in order, up off the floor, and stored neatly in one place so they`re easy to find and put away. Slanted shelves help shoes stay visible, while chrome fences keep them in place. Four of the five shelves are adjustable, so you can move them up or down easily to make room for different types of shoes or boots. The tower is easy to assemble and can be set on the floor or hung on a heavy-duty steel rail to keep floor space open underneath for additional storage.

Shoe Rack

Shoe Rack,Shoe Storage,Shoe Organizer,Wooden Shoe Rack,Storage Cabinet,Shoe Bench

FuJian YuanFu Import&Export Trading Co., Ltd. , https://www.fjyffurniture.com