Abstract: Along with the developing of color imaging technique, the application of digital multilevel imaging device increases, such as digital printing press, color printer, electronic engraver for gravure printing and so on. Based on multilevel halftoning technique, some important items, i.e. count of color element, area percentage of color elements, relationship between the percentages of color element and multilevel dots are studied and summarized. Finally, based on Neugebauer equation, a theoretical color model under the condition of multilevel halftoning is constructed.
Abstract: Image data is always a major fraction of the huge data to be stored or transmitted. That is why researchers have been evolved in finding out different ways and techniques to increase compression rate and reduce information loss. This research investigated the improvement of JPEG compression algorithm by incorporating cubic spline interpolation (CSI) in the sampling stage and four different color spaces in the color space transformation stage. JPEG 1992 standard was considered and results were compared with previous works done by different researchers. The sampling and color space transformation stages of the JPEG algorithm were taken into consideration. In the color space transformation stage, two linear and non-uniform color spaces RGB and YIQ, and two uniform color spaces CIELAB and the CIECAM02 based uniform color space CAM02-UCS were incorporated and investigated. The sampling stage of JPEG contributes much to improve the compression rate at the cost of loss of some information. Current study incorporated cubic spline interpolation technique to reduce the information loss at this typical stage. The CIEDE2000 color difference formula, which is best correlated with the human visual perception, was used as metric to investigate performance of newly proposed improvements in JPEG algorithm for color image compression. The test results showed that the proposed modifications in the two stages of JPEG algorithm improved its performance in terms of compressibility and quality, and the difference in performance was statistically significant. Psychophysical experiments were also performed which validated the test results.
Abstract: This work forms part of large project for measuring the skin colors. This topic has been historically extensively studied due to the strong need from the photographic, digital imaging and medical applications. However there are still many unresolved issues, for example the measuring accuracy and the difference between different measuring methods. The paper focused on one of the measuring methods: camera. The goal is to develop PCA methods to reconstruct the reflectance from images captured by a camera, and the result shows that using three components is enough to acquire high accuracy, and it is possible to have a single skin model to predict all the available skin colors.
Abstract: Color constancy is a key metric for evaluating the color reproduction performance. This contribution proposed a color constancy based spectral separation method for muti-ink printers from the prospect of color perception. Basing on our previously developped spectral printer modeling workflow, a novel color constancy based spectral separation method for muti-ink printers was proposed, which achieved high-level color-constant color reproduction.The experiment results shows that the workflow described in the paper not only could makes full use of device gamut, but also improves the comprehensive color constancy performance obviously. Averagely speaking, the Color Inconstancy Index of reproduced colors is reduced from 2.884 △E00 to 2.016 △E00 , while maintaining reasonable spectral and colorimetric reproduction accuracy.
Abstract: In order to assess the performances of different color rendering index (Ra, CRI, CQS, nCRI, R96a). The LED (light-emitting diode), fluorescent light sources and 30 printed color samples were used in our experiment. 20 observers were organized to carry out the color preference experiment, the visual data were accumulated to test the performances of the light sources and the results indicated that existing color rendering index have some deficiencies to assess the quality of the light source, which were needed to be modified for the theory of color science and industry application. The new CQS additional scales were calculated and the improvements were still insufficient for the LED light sources.
Abstract: In order to improve the quality of prints, we usually add additional OG or RGB ink on the basis of the four-color printing ink (CMYK) to increase the printing color gamut. After that, the conventional separation technology is no longer suit for multi-color printing, so the multi-color separation technology is put forward. Currently, the main multi-color separation method is color partition technology. It divided the color space into five or six partitions. Then each partition was subdivided into several cells, and then established the polynomial color separation model for each cell. In this paper, we improved the selection of samples and cell search method. The experimental results showed that the color separation algorithm had high color separation accuracy and stability and could meet the demand of high precision multi-color printing.
Abstract: Neugebauer printing color model can be divided into tristimulus model and spectral model in form. After color subarea, if these two models are directly applied to multicolor separation, the accuracy of color separation is far from enough. A relatively effective way is to conduct cellular division for device independent color space and achieve higher accuracy through measuring more training samples. This article aims at CMYKRGB seven color separation applications and after performing color separation for two Neugebauer models, cellular divisions with different grades would be carried out successively. The predicted color accuracy of these two models after cellular divisions will be detected using color separation printing test color targets. The impact of cellular division correction on predicted color accuracy and calculation efficiency would be analyzed based on the test results finally.
Abstract: To improve color consistency and accuracy of mobile terminal, a color management system for mobile terminal is built based on color management mechanism of International Color Consortium. It comprises a server-side and a client-side. The server-side consists of a computer, a spectrophotometer and relative programs, providing color measurement and profile generation for mobile terminal. Its programs comprise a communication module, a color measurement module and a profile generation module. The client-side is composed of a mobile terminal and relative programs. Its programs comprise a communication module, a screen calibration module, a screen characterization module and a color conversion module. The two communication modules connect all the other modules of two sides. The color management system for mobile terminal is applicable on any operating systems such as Android, iOS and Windows Phone System.
Abstract: Scan-digitizing is one of the main ways to digitize the original. Building scanner profiles are usual practice to get the consistent color. In the paper, we describe how to get the best possible ‘Raw RGB’ image from a scanner. First we measured the accuracy of those different input profiles. The profile accuracy depends on the relationship between scanner RGB and the corresponding LAB or XYZ values. Then we compared the range of those input profile tones. The ideal tone response curve can be decided by setting the scanner gamma. So a good input profile can faithfully render the dark and murky appearance of an underexposed image or the washed-out appearance of an overexposed one. In order to get a good scanner profile we proposed a method to determine a suitable tone response curve. A new algorithm was then developed according to N-component LUT-based input profile. Experiments were carried out to compare these scanner profiles. The results showed that the ICC profile generated by the new algorithm has obvious advantages in accuracy and grey predicting.