The quality of the prints produced by an ink jet printer is highly dependent on the characteristics of the dots produced by the ink jet pens. While some literature discusses metrics for the objective evaluation of print quality, few of the efforts have combined automated quality tests with subjective assessment. The authors develop an algorithm for analyzing printed dots and study the effect of the dot characteristics on perceived print alignment. The authors establish the perceptual preferences of human observers via a set of psychophysical experiments.

The responses of opponent channels have been modeled in the past as a linear transformation of cone absorption values L, M, S. The authors asked two related questions: (i) which form of transformation is psychologically most plausible and (ii) is a linear transformation the right model, in the first place. The authors tested positions of unique hues for seven subjects in an xy chromaticity diagram as well as in a Boynton–MacLeod chromaticity diagram in log-coordinates. The results show that neither of the two opponent channels can be adequately approximated by a single straight line. The red-green channel can be approximated by two straight lines. The blue-yellow channel can be approximated by a quadratic function, whose middle section coincides closely with the daylight locus. These results show that linear models do not provide an adequate description of opponent channels. Our further analysis shows that there is a correlation between the red and the green directions.

A novel compressing method of high dynamic range image based on fast integrated surround Retinex model is proposed in this paper. The proposed method has two novelties. First, multiscale surround images are integrated to a single surround field, which is applied to center/surround single-scale Retinex (SSR) model. The method reduces the "banding artifact" seen in normal SSR and simplifies the complicated computational steps in conventional multiscale Retinex. Second, the Gaussian pyramid method is introduced to cut the computation time for generating a large-scale surround by tracing a "reduction" and "expansion" sequences using down and up sampling followed by linear interpolation. The computational expense is dramatically saved less than 1/100 for getting a surround by Gaussian convolution with large kernel size. The proposed model worked well in compressing the dynamic range and improving the visibility in heavy shadow areas of natural color images while preserving pleasing contrast.

Mobile displays such as personal digital assistants and cellular phones encounter various illumination levels, different from the flat panel displays mainly used in indoor environment. In particular, in the daylight condition, the displayed images or text on a mobile display can be darkly perceived, which results in the degradation of sun readability in a mobile display. To overcome this problem, we proposed an illumination level adaptive color reproduction method with a lightness adaptation model and flare compensation. Lightness adaptation is a physiological mechanism to shift the photoreceptor response curve according to the illumination level. Thus, as a mobile phone is carried from an indoor to outdoor environment, the photoreceptor response curve automatically shifts toward a higher luminance to adapt to daylight intensity. Consequently, for a lower intensity emitted from the mobile display, the photoreceptor response curve becomes less sensitive, thereby decreasing the perceived brightness of the displayed image. Moreover, colors produced by mobile display can also be influenced by the flare, defined as ambient light reflected from the display panel, which reduces the maximum chroma of the mobile display gamut. Based on these physiological and physical phenomena, the lightness values of the input image are enhanced by making a linear relation between input luminance value estimated by device characterization and photoreceptor response value calculated from the lightness adaptation model. For the chroma component of the lightness-enhanced input image, chroma compensation is conducted by adding the chroma values of the flare multiplied by the enhancement parameter, depending on the hue plane of the gamut boundary. Throughout the experiment, the proposed algorithm not only reproduces bright and colorful images in the mobile display under daylight conditions, but also produces a solution to improve sunlight readability.

Paper for ink jet printing has to obtain optimal printing runnability, printability, and printing quality. Therefore, it must have some specific properties that ensure optimal drying time, mechanical stability of a print, and its light and water resistance. The paper surface should enable the printing ink to be dried as fast as possible. The aim of the applied research was to determine how an ink jet color print on paper changes with time immediately after printing, and how long it takes for the color print to stabilize. Color differences ΔE*_ab were measured that appeared on print after a certain amount of time with regards to values attained immediately after printing. The influence of paper on colorimetric properties and optical density of a print was analyzed by measuring some structural, surface, and sorption properties. The values attained show that the paper surface should enable wetting and ink penetration in paper structure. The biggest changes in colorimetric properties of the print became visible during 1 h after printing; however, color print finally stabilizes only after 96 h. Research results confirmed the importance of paper sorption properties for obtaining high-quality ink jet color prints.

The authors have developed a multi-spectral scanner for accurately printing proofs that employs an LED array coupled with a photodiode array to measure the reflectance spectra. The system is composed of an LED array with five different spectral radiant distributions and 2048 silicon photodiodes with a Selfoc lens array (SLA) for imaging. Five types of LED were selected from among 40 types of commercially available LED with different spectral radiant distributions in order to minimize the average color difference ΔE*₉₄ between the measured and estimated reflectance spectra of 81 typical color charts. The multiple regression method based on the clustering and polynomial regression algorithm was introduced for highly accurate estimation of the spectral reflectance for printing. The results indicate that the average and maximum color differences ΔE*₉₄ between the measured and estimated reflectance spectra of 928 color charts were 1.02 and 2.84, respectively. The scanner can measure the reflectance of prints having a 0.5 mm pitch resolution and a scanning speed of 100 mm/s. The field programmable gate array (FPGA) and digital signal processor (DSP) were introduced in order to accelerate the calculation of sensor calibration and the estimation of the reflectance spectra of the printed proof for practical and commercial use. As a result, the developed scanner could measure the reflectance spectra of the printed proof within 20 s.

In this paper, the analysis methods used for developing imaging systems estimating spectral reflectance are considered. The chosen system incorporates an estimation technique for spectral reflectance. Several traditional and machine learning estimation techniques are compared for this purpose. The accuracy of spectral estimation with this system and each estimation technique is evaluated and the system's performance is presented.

Kaarna et al. [J. Imaging Sci. Technol. 48, 183–193 (2004)] presented a technique based on principal component analysis (PCA) to embed a digital watermark containing copyright information into a spectral image. In this paper, a hybrid watermarking method based on the pure PCA approach of Kaarna <etal/> and singular value decomposition (SVD) is proposed. The performance of the proposed technique is compared with a pure PCA based technique against attacks including lossy image compression, median, and mean filtering. The experiments show that the proposed method outperforms a pure PCA based technique.