Abstract: Active research has been carried out at Leeds over the years to achieve successful colour reproduction. The focus now is on the two extreme reproductions from spectral at one end to preferred at the other end. The former is based on a large sized 12-colorants inkjet printer to achieve accurate spectral match between colour patches. For preferred reproduction, two approaches were carried out: preferred skin colours, and emotion terms such as passive-active, pleasant-unpleasant, cool-warm. Models were developed to fulfill all applications.
Abstract: Color management has been applied in the printing industry since 1993. Press papers as one of traditional substrates, its properties impact the quality of color reproductions. At present, almost all kinds of papers contain OBA. OBA works by absorbing ultraviolet wavelengths of the illuminant, emitting fluorescence at blue wavelengths, increasing the amount of light, and making the paper brighter. This effect of OBA is difficult to measure with common spectrophotometers accurately, which creates a mismatch between color proofing and printing. Furthermore, both the printing standards, as ISO 12647-2 defined substrate without fluorescence. It results in some problems in printing conformance using paper with OBA. This research discovered influence of OBA to color samples, derived colorimetric conversion method to correct and compensate the effects of OBA in papers, and demonstrated the efficient of the colorimetric conversion method in color management workflow with soft proofing.
Abstract: A psychophysical experiment on evaluating of Perceptual Rendering Intent in sRGB v2 and v4 profile as source profiles in ICC printing workflows was conducted. The Perceptual rendering intent in the sRGB v4 preference profile obtained higher scores than that in v2 profile in terms of both preference and subjective accuracy. No single tested workflow performed best on both preference and subjective accuracy. In terms of the observers’ reliability, expert observers had a higher consistency and smaller variance than the naive observers did.
Abstract: As some images perhaps contain pixels whose individual colors will not be perceived if they are below the spatial threshold of human visual system (HVS), the paper presents a wavelet transform method for color image considering HVS characteristics to reduce the redundant color information and then construct perceived gamut of image (PGI), which will be used for effective image-dependent gamut mapping. Taking into account the Contrast Sensitivity Function (CFS) of HVS model, the color information reduction is implemented in some subbands of the wavelet transform domain. Then the image gamut was visualized using the general convex hull algorithm and the constructed PGI will only indicate the perceived part of color image. We preliminarily establish a method for reliably determining PGI, which is help to developing robust and psycho-visually justified image gamut mapping algorithm in the future.
Abstract: The goal of the work proposed in this dissertation is to develop a new method for the chrominance measurement and predict the spectral reflectance. Since the special feature of the holographic paper, it can reflect rainbow colors when it is in daylight, and the chrominance and the density of reflected light would change along with the observation angle changing, so when ink is printed, the chrominance and the quality of the products are difficult to detect. In this paper, we followed the convention of radiometry, derived the light distribution regular model of the interaction of light when it printed on holographic papers, and derived a new model to detect the chrominance information by changing the illumination condition. Finally, we established a spectral reflectance model by considering on the propagation of light.
Abstract: we proposed a model for reflectance of a medium in ink layer. And the scattering coefficient is more complicated than the refractive index and absorption coefficient due to its complicated scattering laws and multi-direction, and the multi-direction makes different scatting coefficients in different situation. The goal of the work proposed in this dissertation is to develop a new method to analysis the scattering situation using random walk. By analysis the probability of the scattering of the particle, we obtain the reflectance factors of the diffusing medium with the observation geometry. The present model enables one to predict the reflection spectrum of a particle medium, then to estimate the color and brightness.
Abstract: The conversions of color spaces are core techniques of modern ICC color management and the study of color space conversion algorithm between L*a*b* and CMYK is valuable both in theory and in application. In this paper, firstly ECI2002 standard color target data are uniformly selected, including modeling data and testing data; secondly the models of color space conversions from CMYK to L*a*b* and from L*a*b* to CMYK are built based on Radial Basis Function (RBF) neural network; finally the precision of the models are evaluated. This research indicates that the RBF neural network is suitable for the color space conversions between CMYK and L*a*b*. The models’ building processes are simpler and more convenient; the network has fast training speed and good results. With the improvement of the modeling method, this method for color space conversion will have a broader application.
Abstract: The efficient reconstruction of spectral color information was the key research subject of color production technique based on spectrum. For the reality that the current principal component analysis method and independent component analysis method cannot solve the efficient reconstruction of spectral color information satisfactorily, it put forward the mixed frequency component analysis method in the integrated and unique perspective for the first time. And it solved the efficient reconstruction of spectral color information successfully, besides it provided the further theoretical support of color vision stage theory and a new theoretical explanation of eye color visual constancy
Abstract: Uncertainty evaluation of spectral color measurement is the best method of evaluation of color measurement result’s quality. Firstly type A and type B uncertainty of spectral reflectance are analyzed based on different uncertainty's sources, secondly uncertainty of chromaticity parameters are calculated based on spectral reflectance’s uncertainty. Lastly practicability of uncertainty evaluation of spectral color measurement is proved by experiments.