Effects of fluctuations of the imaging medium in and out of the focal plane (misfocus) are analyzed for laser photothermal imaging materials. Static and dynamic misfocus conditions degrade image quality by producing fluctuations in the imaged spot sizes. A theoretical model is developed for Gaussian profile laser pulses, and for uniform (top-hat) profile pulses delivered by a laser diode. Conditions which maximize the depth of focus are determined. The depth of focus can be made arbitrarily large by wasting laser energy. The maximum depth of focus for limited laser energy is found to be slightly above the fluence needed for imaging with maximum efficiency. Experimental results are presented for four different imaging media. One simple medium with a thin metal film on a clear polyester substrate, agrees almost perfectly with the theoretical model and therefore behaves “ideally”. More complicated media with other substrates and other surface layers, are shown to deviate from the theoretical model due to nonlocal behavior. Nonlocal behavior means laser energy incident on one region affects nearby regions. It is shown that purposely designing nonlocal behavior into imaging media can improve the depth of focus, in some cases by factors of two or three.
In doing research for developing future digital products, we have analyzed worldwide management data at our disposal that pertains to analog plain paper copiers (PPCs). According to our copy volume data, average monthly copy volume is proportional to the square of the speed (copies per minute) of PPCs. The result of our analysis of the copy volume data provides new information relating to such factors as the scale of offices and the workflow within them (factors influencing average monthly copy volume). The shift in the information infrastructure from a copy-and-distribute to a distribute-and-print model is discussed. According to our field service data, mean copies between service visits is proportional to the half power of the average monthly copy volume. The result of our analysis of the field service data provides new information relating to such factors as the level of technology represented by each PPC series (influencing mean copies between service visits). The copy volume business with field service in the copy market is discussed in light of our new knowledge about both copy volume and product reliability.
In the electrophotographic process, electric fields are used to detach and move charged toner particles from one surface to another. In principle, electric field detachment occurs when the applied electrostatic force overcomes the toner adhesion force to a surface. For triboelectrically charged toner, many measurements have indicated that the electrostatic adhesion force is much greater than that calculated for a uniformly charged dielectric sphere, suggesting that the surface charge distribution on a toner particle is nonuniform. In the present work, the physics of the electrostatic force is described and a dumb-bell type charge distribution on triboelectrically charged toner particles is proposed as an approximation of nonuniformly charged particles. The electrostatic force on an isolated toner particle with a dumb-bell type charge distribution is computed by means of a recently developed computational method based on a Galerkin finite-element technique. The effect of the electrode spacing on the electric field detachment of charged toner particles is examined in particular. The results show that the magnitude of electrostatic force is rather insensitive to the electrode spacing when the particle is nonuniformly charged, unless the spacing is so small that the counter electrode is nearly touching the particle. The electrostatic force for detaching a charged particle is shown to become maximized when the particle charge and applied field strength satisfy a certain relationship. Formulas are also derived for the minimum electric field strength and the corresponding particle charge that are required for the maximized electrostatic detaching force to overcome the non-electrostatic components of adhesion. For triboelectrically charged toner particles, the components of the electrostatic force components are shown to be much greater than nonelectrostatic force components. If the particle charge is proportional to the particle surface area and the non-electrostatic force component is relatively insignificant, the detachment of toner particles in response to an applied electric field should be independent of the particle size.
In the most popular toner fusing process, toner melts are fused onto the paper under the influence of heat and pressure exerted by the nip forming rollers. The degree of toner penetration influences the toners fuse level and depends on process conditions, toner rheological and paper properties. This article establishes a three-dimensional (3D) model for studying toner penetration onto the paper macroscopically. The model considers a toner melt layer sandwiched between a smooth fuser roll and a porous paper surfaces under heat and pressure. Toner penetration and their thickness variation within the nip are computed under various conditions of toner viscosity, paper permeability, applied pressure, dwell time, and toner layer thickness. Toner viscosity is a strong function of temperature. Under normal fusing conditions and using Xerox 4024 plain paper, toner images just fill the voids at the paper surface. Only the less viscous liquid, such as fuser oil, can easily penetrate into the paper. Modeling results compare favorably with the actual toner images. The model can be applied to other penetration studies also.
The photochemical reaction of dichromated gelatin solution in the spectrally sensitized region was investigated under normal room conditions employing a water-soluble gelatin. Sample solutions containing dichromate, gelatin, methylene blue (MB) and pH buffer solution, were exposed with the light limited to longer wavelength than the intrinsic sensitive region of dichromate. The decrease in absorbance for the photoreduction of Cr(VI) was monitored by UV-visible spectroscopy. For comparison, ethylenediamineacetic acid (EDTA) was used as a reducing agent. It found that the reaction order, pH dependence of reaction rate, and activation energy differed both when gelatin and EDTA were compared. On the basis of experimental observations and discussion, a mechanism and its rate determining step were proposed.
A novel model related to triboelectric charging phenomena in toners containing charge control agents (CCA), used as marking materials in copy machines in electrophotography, is proposed. The model was evaluated by comparing the results from computer chemistry using the molecular orbital method (MO), molecular mechanics method (MM), and Monte Carlo method (MC), with the results from measuring triboelectric charge of several toners containing various CCA. The model is based on the interaction of water molecules and CCA molecules. The CCA is divided into two reciprocal polarity regions in the molecule; one region with the same polarity as the CCA charge and another region with the contrary polarity to the CCA charge. The two regions play different roles in CCA toner charging phenomena. Therefore, the polarity and magnitude of the charging is determined from balancing the intensity of interactions among the each region in the CCA molecule and the water molecule. The consequence of molecule structure of CCA to toner charging is elucidated.
Image capturing systems generally fall into two broad categories: silver halide photography and digital imaging equipment. Each has advantages and disadvantages; a user must select the method that best suits his needs. The authors of this article are conducting research and development into a new image capturing method called Elgraphy that combines electrophotography and liquid crystal technology. It has the advantages of being a dry system, and having a high resolution and high sensitivity. Efforts are being made to establish a new imaging technology that exploits the characteristics of Elgraphy.1–4 This article provides an overview of the new image capturing technology; details will appear in subsequent articles.
In digital photography, input photoimages to the electronic camera are sampled by segmental imager and converted into image data. The smallest unit of division is called a pixel and the segmentation fixes the size and number of those pixels. Output picture definition is directly related to the pixel number of the input imager. Moreover the image processing to modify the pixel condition influenced the tonal quality of output image. This article discusses the relationship between the conditions of pixel in the imager of the input digital still cameras (DSC) and the image quality of output prints in a digital photography system. Sample color prints showing the same test pattern images in different definition proportional to the numbers of pixel were produced by a single digital photography system. The correlation between the pixel condition of input device and the structural and tonal image quality of output prints were apparent to the subjective visual examination and the objective physical analyses. The effects of pixel condition appeared in the drastic MTF changes on the image structure and the apparent definition changes on the tone rendition of reproductions on the sample prints. The results suggest that there is a limiting pixel number for digital cameras to produce satisfactory hand-held size digital photography color prints.
The objective of image reproduction is, as used here, to reproduce visual information that is available in the original image. Undoubtedly, the colors of the individual pixels contain a huge amount of visual information and therefore the quality of the image reproduction is typically studied in terms of the quality of the color reproduction determined for each image pixel. It is, however, true that not only the colors of the individual pixels but also the spatial structures formed by the color fluctuations across the image are very important sources of visual information. Because only minor errors in the color reproduction may cause significant errors in or even vanishing of the spatial structures of an image, they both—the reproduction of the color and the reproduction of the spatial structures—have to be analyzed to determine the quality of the image reproduction. There are commonly accepted methods for the quality analysis of color reproduction. A quality analysis for the reproduction of the structures is developed in this study. Three metrics, selected on the basis of the monocular sources of visual information, are used to describe the spatial structures of the original and the reproduced images. The metrics—the edge contrast, the size of detail and the evenness contrast—are analyzed by using the methods of binary and gray morphology. The use of the metrics in the quality analysis of the image reproduction is illustrated by computer simulations.