This article presents a comprehensive study on the spectrum-based color reproduction system, called Natural Vision (NV), which aims to break through the limitation of red–green–blue (RGB) three-primary schemes. After a basic discussion on the motivation for color imaging technology beyond RGB, the method for systematizing the multispectral and multiprimary color imaging technologies, including image capture, processing, storage, printing, and display, is presented. Then experimental multispectral systems for both still image and video are introduced, and the following features of spectrum-based scheme are revealed: a) highly accurate color reproduction is possible even under different illumination environment, b) an expanded color gamut can be reproduced by multiprimary color displays, c) the influence of observer metamerism can be reduced by the spectral color reproduction, and d) the quantitative spectral attributes of an object, useful for its analysis or recognition, can be captured and preserved. Finally, the effectiveness of the system is also demonstrated through experiments in fields of application, such as medicine, digital archives, color printing, electronic commerce, and computer graphics.

Colorization algorithms, which hide color information in gray images and find them to recover color images, have recently been developed. In these methods, it is important to minimize the loss of original information while the color components are embedded and extracted. In this article, we propose a colorization method using a wavelet packet transform in order to embed color components with minimum loss of original information. In addition, the compensation processing of color saturation in the recovered color images is achieved. In the color-to-gray process, an input red-green-blue image is converted into Y, Cb, and Cr images, and a wavelet packet transform is applied to the Y image. After analyzing the amounts of total energy for each subband, color components are embedded into two subbands including a minimum amount of energy on the Y image. This makes it possible not only to hide color components in the Y image, but to recover the Y image with minimum loss of original information. In the gray-to-color process, the color saturation of the recovered color images is decreased by the printing and scanning process. To increase color saturation, the characteristic curve between printer and scanner, which can estimate the change of pixel values before and after the printing and scanning process, is used to compensate the pixel values of printed and scanned gray images. In addition, the scaling method of the Cb and Cr components is applied to the gray-to-color process. Through the experiments, it is shown that the proposed method improves both boundary details and color saturation in the recovered color images.

The interaction between paper and toner depends on paper properties (roughness, paper surface, and tension) and toner properties (granulometry and chemical composition). Deepening the knowledge on fixation and adhesion of toner onto the paper substrate is crucial to improve the end-use properties of paper dedicated to electrophotographic printing. The aim of this article is to introduce and describe a new tool to visualize and analyze this interaction. Three-dimensional (3D) imaging is a key tool used to investigate such a phenomenon. For this reason, synchrotron x-ray microtomography (SXRM) was applied to characterize the toner-paper interaction in a noninvasive and nondestructive manner. To validate the feasibility of such means in a 3D context, the obtained data are compared to those obtained by traditional two-dimensional (2D) imaging systems such as optical profilometry and environmental scanning electron microscopy. SXRM emerges as a crucial tool to get a detailed characterization of the ink layer and of the ink-paper interaction. This is a powerful technique to complete studies carried out by classical means.

Particles of electrophotographic toner (black, silica-coated, number-weighted diameter of 7 μm) were electrostatically developed on the surface of a film of bisphenol-A polycarbonate coated on nickelized polyethylene terephthalate (PET). The thickness of the coatings varied from 0.8 to 22.0 μm. The force needed to remove the particles was determined using ultracentrifugation. We found that removal of half of the particles from the film surface required a force of approximately 250 nN irrespective of the thickness of the polymer film. This result indicates that removal of the toner from the film involves surface van der Waals interactions rather than forces associated with long-range electrostatic interactions of the charged toner with the grounded nickel electrode.

Gloss development is known to be different in offset printing and electrophotography. Gloss is also known to be determined by the topography, namely the three-dimensional profile, of the printed surface. This study aims to shed light on the difference between surface topography formation processes in offset printing and electrophotography. Our observations showed that in offset printing, printed surface topography forms through the following process: Upon ink transfer, the ink surface is uneven due to inhomogeneous ink layer splits. This unevenness is leveled out over time. Ink flows along the paper surface and the ink vehicle penetrates into the paper, thus yielding a printed surface topography consistent with the original paper surface topography. In electrophotography, printed surface topography was shown to form through the following process: Before fusing, roughness distribution along the unfused surface is characteristically similar to that of the paper surface. Pressure and heat applied upon fusing cause the toner to spread sideward, thus yielding a printed surface that is different from the original paper surface topography; more specifically, the printed surface becomes smoother than the paper surface. We then incorporated into electrophotography the processes which in offset printing appear relevant to formation of a printed surface topography that follows paper surface topography. This method of electrophotography produced a printed surface topography and print gloss more consistent with the paper surface topography.

The demands for high electrophotographic color print quality emphasize the importance of the paper surface. This work demonstrates the effects of the surface roughness and coating layer characteristics of low grammage coated papers on print mottle. Samples were prepared using different coating techniques, different coating formulations and different coat weights and by changing the calendering conditions to give different surface morphological properties. Print mottle was strongly dependent on substrate roughness. The impact of the surface topography was further demonstrated at different transfer voltages, and when the moisture content or resitivity of the paper was changed, where significant differences were found in print mottle especially when the paper was rough. Surface topography can be optimized by a suitable combination of surface treatment and finishing parameters to give a surface texture with good toner-recipient properties.

An ink jet printer was used to deliver small quantities of ink-dyed water to laboratory handsheets having a range of compositions and treatments. An optical profilometer recorded initial and final roughness statistics at fixed locations on the printed surfaces. For paper made with chemical pulp, it was found that the relative change in local roughness after rewetting (change in roughness divided by initial roughness, ΔR_a/R_ao) increased with the degree of calendering, beating, and the amount of surface and internal sizing. The corresponding changes in skewness and kurtosis after rewetting reflected the development of increased fiber rising. Increasing amounts of surface sizing produced larger ΔR_a/R_ao, corresponding to an increase in the ink penetration depth. Rewetting produced the greatest ΔR_a/R_ao in paper manufactured with mechanical pulp, with ΔR_a/R_ao becoming smaller as the fraction of chemical pulp was increased to 0.4, after which it became insensitive to composition.

The article discusses changes that occur when paper samples printed with an office ink jet printer HP 5550 are exposed to elevated temperature and relative humidity without the presence of light for a prolonged time period according to accelerated artificial aging standard EN ISO 5630-3. The effects of paper coating pigment type (pyrogenic silica, precipitated and ground calcium carbonate) and the amounts of binder and dye fixative on print quality and darkfastness are examined. Results show that both color chroma and print density of prints made with the dye-based inks–cyan, magenta and yellow–on calcium carbonate coatings are higher compared to coatings where silica is used. The opposite is true for the black pigment-based ink where silica clearly outperforms calcium carbonate coating pigments. Accelerated artificial aging deteriorates color vividness much more severely with ground CaCo₃ than with precipitated CaCo₃ coatings, while prints on silica coatings exhibit the highest darkfastness.

This article proposes a novel architecture of high selection speed three-dimensional data registration circuit for ink jet applications. With the configuration of three-dimensional data registration, the number of data accessing points as well as the scanning lines can be greatly reduced for large array ink jet printheads with nozzles numbering more than 1000. This integrated circuit architecture involves three-dimensional multiplexing with the provision of a gating transistor for each ink firing resistor, where ink firing resistors are triggered only by the selection of their associated gating transistors. Three signals: selection, address, and power supply, will be employed together to activate a nozzle for droplet ejection. The total number of data accessing points of the three-dimensional configuration will be the cubic root of the nozzle number with each jet controlled by five input lines, including multiplexing data latches and shift registers. The simulation and experiment results demonstrated a reduction of scanning time by up to 67% thanks to the reduction of lines for scanning when compared to a two-dimensional configuration. The total circuit area, 2500×2500 μm², will be 80% of the circuit area by three-dimensional configuration for 1000 nozzles. This device has been designed, fabricated by CMOS 0.35 μm process, and characterized.