The authors used a simple model and a prototype machine to study statics and dynamics of a magnetic brush in a two-component development system in electrophotography. In the model experiment, the authors measured the normal and tangential forces of the brush formed from a chain of magnetic carrier particles when it comes in contact with the photoreceptor to clarify the relationship between the tangential friction force and the diameter of the carrier particles, magnetic flux density, and the length of the brush. The tangential friction force increased with the magnetic flux density and decreased with an increase in the length of the brush; however, the total force was unaffected by the diameter of the carrier particles. On the other hand, numerical calculations performed using an improved distinct element method revealed that although the total force was not affected by the diameter of the carrier particles, the individual differential force acting on the magnetic particles of the chain was small, and the density of the carrier particles that come in contact with the photoreceptor drum was high when the size of the particles was small. In the investigation carried out using the prototype machine, it was found that the magnetic brush formed in the development area is inclined in a direction parallel to the magnetic field and that the chains are crushed by the photoreceptor drum. Although the total pressure applied on the photoreceptor was almost independent of the diameter of the carrier particles, the differential force exerted by individual chains is small and distributes dense when the size of the particles is small; on the other hand, it is large and distributes rough when the size of the particles is large as predicted by the model investigation. This result suggests that small carrier particles are advantageous in preventing any disturbances in the images developed on the photoreceptor. The effects of the development gap and the thickness of the layer of supplied carrier particles have also been evaluated.

Image compression schemes facilitate the transmission and storage of data in an efficient form by reducing redundant image data in the case of limited transmission bandwidth or storage space. However, due to the irreversible nature of lossy compression, these schemes also introduce various types of color artifacts into the reconstructed image at a high compression ratio. Consequently, a change in color information affects the gamut characteristic of the reconstructed image. Accordingly, this article investigates the relationship between the compression ratio and the gamut variation for a reconstructed image using JPEG and JPEG2000. To analyze the relationship between the compression ratio and the gamut variation, 18 color samples from the Macbeth ColorChecker are initially used as representative colors for all colors due to their uniform distribution in CIELAB color space. Based on the color information shift for representative color samples, 12 natural color images, classified into two groups depending on four color attributes, are used to investigate the relationship between the level of compression and the variation in the gamut area for reconstructed images. After determining the gamut areas for the decompressed images in relation to the compression ratio, gamut fidelity is obtained using the ratio of unique colors relative to the gamut area. Finally, the optimal least square method is applied to obtain fitted curves as an equation minimizing the error between the real data, the gamut area for the decompressed images, and the corresponding approximated values.

This article analyzes the spectral reflection properties of skin surface with make-up foundation. Foundations with different material compositions are painted on a bioskin. First, the authors measure the spectral reflectance of the skin surfaces under a variety of conditions of light incidence and viewing. Second, the authors show the limitations of the model-based approach for describing the reflectance curves by a small number of parameters. A new approach based on the principal component analysis is then proposed for describing the detailed shape of the surface-spectral reflectance function. All skin surfaces exhibit the property of standard dichromatic reflection, so that the observed reflectances are expressed as a linear combination only two spectral components of a constant reflectance and a diffuse reflectance. Moreover, the authors find that the weighting coefficients are decomposed into two basis functions with a single parameter. As a result, the spectral reflectance under arbitrary observation conditions can be estimated by synthesis of the diffuse spectral reflectance and several one-dimensional basis functions. Finally, the feasibility of the proposed approach is examined in detail in experiments using real foundation samples.

In this research, the authors have developed a compact and fast measurement system for three-dimensional (3D) shape, normal vector, and bidirectional reflectance distribution function (BRDF) of a 3D object, e.g., a human face. Since the proposed system uses linear light sources and a luminous intensity distribution of these light sources, the BRDF can be measured for a short time and without large measurement space. The proposed system is evaluated by two methods whereby the authors confirmed its accuracy: by measuring sample known objects and by comparing actual and reproduced images.

To assist with the color system design of a four-primary color display, it is necessary to build up a four-primary color simulation platform displayed on a wide color gamut red, green, blue (RGB) monitor. A new four-primary color conversion algorithm that is able to simulate four-primary color appearance built on a wide color gamut RGB monitor is proposed. The designed four-primary color system is composed of red, green, blue primary colors based on sRGB standard and the addition of the fourth primary color. The simulated fourth primary colors are selected from Kodak Wratten color filters, which CIE U'V' chromaticity coordinates are located in the range between the sRGB triangle gamut and the Adobe RGB (1998) triangle gamut. The four-primary color conversion algorithm is designed to be implemented on the Adobe RGB (1998) platform to simulate four-primary color appearance. The linear programming to formulate the convex optimization problem, which is named linear color convex combination, is introduced to establish a color conversion algorithm between the four-primary color signal and the corresponding color stimulus. The four-primary color conversion is also applied to build up four-color separation channels, which can simulate four-color channels shown on the Adobe RGB (1998) platform. It is demonstrated that the proposed color conversion algorithm can perform well on four-color channels displayed on the Adobe RGB (1998) platform. Meanwhile, the optimal four-color signals can be determined according to the tonal smoothness evaluation based on edge detection by Prewitt or Sobel operation.

Spectral imaging is becoming popular. Spectral accuracy in measurements is an important factor, especially now when fluorescent and light emitting diode (LED) based light sources are becoming common. Browsing image sets in a modern network is also becoming relevant, but the problem with spectral data is that the file sizes are so large. An efficient compression method suitable for browsing purposes consists of principal component analysis with spatial subsampling. In this study, the optimal combinations of a sampling interval and parameters of the developed compression method are found for different data sets under several light sources. It is shown that depending on the light source, 3–20 nm sampling intervals are required. In addition, with different light sources and data sets, between three and six principal components must be used. With a suitable spatial subsampling mask, high compression ratios can be achieved with good results. The spatial subsampling is a fast operation and can be done online before transmission, which gives the client user a possibility to choose the compression ratio.

Digital printing has focused on multilevel dithering using a stochastic screen as this procedure is simple to implement and yields a smooth output pattern. In bilevel halftoning with a stochastic screen, two printable output levels, i.e., black and white, corresponding to the input image, values are determined by the threshold values of the stochastic screen. For multilevel halftoning, these threshold values are then simply extended using a scaling function. Yet, a simple extension using a scaling function also generates banding artifacts around the intermediate printable tone levels, producing discontinuity in a smooth tone transition region. Therefore, to reduce these banding artifacts, this article proposes blue-noise multilevel dithering with interweaving dot dispersion. First, to investigate the cause and characteristics of the banding artifacts, multilevel halftoning using a simple scaling function is analyzed using a probability model when varying the number of tone levels, thereby generalizing the characteristics of the banding artifacts. The scaling function for the multilevel halftoning is then modified using two control factors based on the generalized characteristics of the banding artifacts according to the number of printable tone levels in order to interweave dot dispersion in the banding regions. The dot distribution across the banding regions is affected by the two control factors that control the interweaving point. The specific values for the control factors are determined by investigating via subjective observation and the human visual system weighted root mean squared error (HVS-WRMSE) curve using the perceived root mean square and based on characteristics of the human visual system. In experiments, an objective evaluation using the HVS-WRMSE of a multitoned image is used to compare the quality of the multitoned patterns around the intermediate tone levels. The proposed method is found to moderately reduce the banding artifacts in the gray ramp when compared to the conventional methods.

Digital data storage on microfilm is a highly attractive technology for archiving of digital data. Its estimated storage lifetime of up to 500 years outperforms conventional storage media such as CDs, DVDs, hard drives, or magnetic tapes. Today, migration is widely used as a solution for long-term data storage but unfortunately also requires costly and time-consuming migration steps. Microfilm offers migration-free data storage and also further advantages as the uncomplicated technology of reading devices and hybrid storage of analog and digital data on the same medium. Due to its write once read many character, it is inherently forgery-proof and safe against virus attacks. This article describes the underlying technology of digital data storage on microfilm, including laser recording, error correction codes, and important system parameters. Possible storage capacities are pointed out and potential applications as well as future developments are described.