Abstract: Based on comparison of spectrum models, this paper chose CYNSN spectrum model as the study object, spectrum prediction as the main study content, the best model parameters’ acquisition as the aim, RRMS and GFC as the evaluate parameters of prediction accuracy. This paper designed the experiment, training samples and test samples to measure and calculate the parameters by programming: Ai (effective dot coverage ratio of the i-th Neugebauer primary), Rλ, i (spectral reflectivity of the i-th Neugebauer primary), n (Yule-Nielsen coefficient) and cell (cell number). The result of experiment and calculation shows that the best n value is 2.8 and cell number is 6. The result of CYNSN Model’s Color Spectrum prediction Accuracy shows that the average RMS is 0.0002, the max RRMS is only 0.0005, the GFC value is approximately 1, that is to say the CYNSN model achieved the better spectrum prediction accuracy after setting the best value of parameter.
Abstract: In the multi-color printing, the four inks used are cyan, magenta, yellow and black, which have different response in the near infrared spectral area, in which the black with CMK color inks have no response while the black with K color ink has a good response. But two kinds of black are both visible and equivalent under daylight. Based on this principle and gray component replacement (GCR) theory, this paper introduces a black component generation method for black ink hiding infrared security image. Firstly, we establish a color lookup table for GCR and find the substitution relation between K and CMY. Secondly, the source image is color-separated with the mask which is the security image. The source image is firstly converted to CMY color format data words. The black value of each pixel for security image is detected and treated as GCR value of the corresponding pixel for source image. Then CMY values are found in GCR LUT and subtracted from three primary CMY values. And an adjustment coefficient is employed for color correction. Thirdly, the color separation image is printed. In daylight the visual effect of printed image is the same as that of source image, but the security image is detected by IR camera. Finally, a series of experiments are performed on HP Color LaserJet CP2035 printer. Experimental results show that the proposed method is promising and feasible for black ink hiding IR security image.
Abstract: The spectral representing accuracy with different wavelength range and sampling interval were analyzed in this study. The spectral reflectance of different color sets were measured. The CIELAB and CIEDE2000 color differences under CIE standard illuminants and actual lighting sources were calculated to evaluate the representing accuracy among the spectral reflectance with various wavelength ranges and sampling intervals. Results of the experiment indicate that the representing accuracy of the spectral reflectance with different wavelength range and sampling interval were affected by the media type. As a whole, the colorimetric representing accuracy of the spectral reflectance with the range of 400 to 700nm and 10nm~30nm sampling intervals are acceptable comparing to the 380 to 780nm range and lower sampling intervals.
Abstract: In order to study the visual characteristics of the human eye on color-distinguishing threshold levels, an experiment, of which the results provide significant data reference and theoretical basis for improvement of color evaluation methods of printing products, was carried out with 20 observers whose visual characteristics are normal. The observers were provided 5 basic colors that the CIE recommended for color evaluation study, and the constant stimulation psychophysical method was used in the visual experiment. The color patches were printed out with small color threshold variations. The color-distinguishing thresholds and visual characteristics were obtained through the experiment. Results showed that the notable color threshold values of green and red patches were relative larger, indicating larger visual tolerances. It is also shown that the red region in CIELAB color space has the best uniformity to human eyes among the five colors.
Abstract: The formation of color images are generally divided into two methods: additive color imaging based on color light mixture and subtractive color imaging based on colorant mixture. Additive color imaging refers to the color image mixed by a certain percentage of the three primary color lights: red (R), green (G) and blue (B), such as LED display, cell phone screens, digital cameras and others. Subtractive color imaging refers to the color image generated by light mixture reflected by each colorant, due to some light of different wavelength in the white light separately absorbed by certain colorant after mixing a certain percentage of the three primary colorant: cyan (C), magenta (M) and yellow (Y). Inkjet, color laser printing, inkjet printing, etc. belong to the subtractive color imaging. Most commonly, printing also belongs to the subtractive color imaging. This thesis is based on the characteristics that fluorescent materials can produce colors under UV excitation, designing and preparing three fluorescent inkjet inks which can respectively produce red (R), green (G), blue (B) under UV light excitation, using inkjet printers to print color images, investigating the imaging mechanism of the additive color based on fluorescence inkjet printing, and observing the imaging results. The results show that color effect of monochrome image is good, and the color deviation is large after overlapping different colors.
Abstract: Image-dependent color gamut mapping can avoid over compression of the image gamut, so it is able to protect the accuracy in color transfer. The premise of realizing image-dependent color gamut mapping is to determine the image color gamut boundary quickly. Now several techniques for the computation of gamut boundary have been presented in the past, e.g. the convex hull algorithm and the segment maxima algorithm. However, the printing image tend to have a higher resolution, it can be very slow and less efficient while using these methods to determine the image gamut boundary. In this article we will introduce a new pre-processing method based on volume rendering to process the image data to improve the speed of gamut visualization.
Abstract: In order to get optimum color reproduction results on different color devices in color management, a proper rendering intent should be selected according to color characteristics of the image. In terms of differences on color characteristics, images could be classified into synthetic graphics and natural pictures. Different rendering intent should be applied on graphics and pictures. So graphic/picture automatic classification becomes a fundamental task of color management intellectualization. Characteristics on color distribution of a large number of images have been researched in our experiments. Then it is confirmed that the essential difference between graphic and picture is the characteristics on color distribution in the neighborhood of images rather than the number of colors or the volume of image gamut. Thus, the features which have distinct ability to show the differences could be used to build classification rules. In this paper, several mathematical features of image are extracted and selected by their classification performance. Based on these features, the discriminant analysis is adopted to build up discriminated functions. Finally, the accuracy of the functions has been tested and the precision is 96.75%.
Abstract: As color gamut of digital output device greatly affects image appearance, accurate and effective gamut description for output device is intensively required for developing high-quality image reproduction technique based on gamut mapping. In this paper, we present a novel method to determine color gamut of output device by using a specific 3D reconstruction technology and device ICC profile. First, we populate the device color space by uniform sampling in the RGB 3-Dimensional space, and convert these sampling points to CMYK color space. Then, we work out the CIE LAB value of these points according to the ICC profile of output device. At last, in CIE LAB color space the boundary of these points is determined by using a gamut boundary descriptor based on Ball-Pivoting Algorithm (BPA) proposed by Bernardini. Compared with the results generated by ICC3D, our proposed method can compute device gamut more efficiently and at the same time give a more accurate gamut description of the output device. It will be help to develop effective gamut mapping algorithms for color reproduction.
Abstract: Yule-Nielsen neugebauer spectrum(YNSN) model can describe the relation between dot area and spectrum reflectance, which can calculate the effective dot area. The modified index in the model still can’t be determined. The reciprocal of paper’s spectral reflectance at the range of visible light is adopted as the modified index in YNSN model in order to reduce the optical dot gain. By experiment, the modified YNSN mode can be used to calculate the effective dot area of light color. The research has a certain significance for controlling and testing printing color.