Abstract Depth map extraction or estimation is very important for many computer vision applications. However, this process involves high cost. Hence, it is interesting to find new approaches, which could yield faster implementations, when very accurate results are not necessary. These new implementations can be built up for the stereovision problem, taking advantage of the specific geometrical constraints of this kind of problem. The problem is solved by searching pixel-by-pixel matching in horizontal lines. In this article, we propose a novel approach to this problem, providing measurements of the processing time and accuracy achieved, as well as a qualitative comparison with other methods available in the literature. The results obtained could reach speeds around one order of magnitude faster than those proposed in other classical implementations. Thus, the proposed algorithm can run on cheap and low-performance hardware achieving real-time processing rates.

Abstract A new method that makes possible a potential profile measurement of an electrostatic latent image is proposed. When the surface potential is greater than the acceleration voltage of the primary electron, the velocity becomes zero before the electron hits the sample. As a result, the primary electron reaches a detector without reaching the sample. The surface potential profile can be measured by detecting primary electrons while changing the applied voltage to the substrate of a photoconductor. The significant feature of this method is that the charging, exposure, and detection devices are all incorporated in the same system, making real-time measurement possible. In order to confirm the phenomenon of reciprocity law failure, the potential depth of the latent image was measured by changing the delay time when double-pulse exposure was carried out. As a result, the latent image potential tends to be formed deeper as the delay time becomes longer. The developed Electrostatic Latent Image Measuring System (ELIMS) has good performance with a measurement potential resolution of 2 V.

Abstract Modern digital copy machines are being designed to run at increasingly higher speeds. In this article, the authors analyzed the thermal and moisture content profiles and their evolution in paper sheets during the fusing process. The thermal parameters for the paper sheets necessary for the model were obtained by independent measurements. Model predictions for the evolution of sheet temperatures were compared with experimental measurements in a commercial large print run copier in order to establish the validity of the model. Sheet temperatures on the image and reverse sides were measured at different points in a continuous run Xerox photocopier. Sheet surface temperatures depend on basis weight, caliper, coating level and filler levels. Coated or highly filled sheets showed higher temperatures, which persisted for longer times, whereas those of lower densities were cooler. Moisture redistribution effects within the short time scale of fusing were insignificant.

Abstract The correction of faded colors in old pictures, prints, and paintings is an interesting issue for color image processing. Several techniques have already been introduced to enhance faded color images, many of which approach the problem as color cast removal and use global illuminant estimation methods, such as the gray world or Von Kries assumptions. However, the use of simple global operators to eliminate the illuminant effects is not always suitable for enhancing faded images. Therefore, this article presents a color correction algorithm based on a multi-scale gray world algorithm for faded color images. First, the proposed method adopts a local process using multi-scale filters, and coefficients are obtained for each filtered image. Integration of the coefficients using weights is then performed to calculate the correction ratio for the red and blue channels in the gray world assumption. Finally, the corrected image is obtained by applying the integrated coefficients to the gray world algorithm. In experiments, the proposed method is able to reproduce corrected colors for both wholly and partially faded images, in contrast to previous methods. The proposed method also enhances the visibility of the input images using multi-scale processing.

Abstract RGB display devices with a white channel have recently been developed to produce a high brightness with low power consumption and enhance the image contrast. However, the addition of a white channel can change the perception of the color represented on the display device because visual adaptations in human are affected by this addition. Although the measured chromaticity coordinates of a color represented with and without a white channel remain the same, the perceived hue is changed. Therefore, this article presents an analysis of the hue shift phenomenon and proposes a hue correction method to provide perceptual color matching between a DLP projector with and without a white channel. To quantify the hue shift phenomenon, color patches are generated at equally spaced hue angles and then individually displayed by a projector and on a CRT monitor. The patches on the CRT monitor are reproduced through device characterization to have an equal colorimetric value with the same patches displayed by the DLP projector with no white channel, so that the patches appearing on the CRT monitor can be used as reference images. Next, the hue for each patch displayed by the DLP projector with a white channel is adjusted by observers until each patch appears the same as its reference image. These adjusted hues are then fitted into three sets of piecewise polynomial functions, which represent the amounts of hue shift required for perceptual color matching. After analyzing the hue shift phenomenon, the RGB for each pixel in the input image of the projector is converted to CIELCh color space to obtain the corresponding hue. This hue is then shifted by the proposed polynomial functions which model the hue shift by adding a white channel. Finally, the corrected hue is inversely converted to RGB in the output image.

Abstract In this article, we propose an edge-directed switching median filter that considers the local correlation of pixels and edge directions for impulse noise reduction. The proposed algorithm consists of two main steps, detection and correction. In the first step, the impulse noise is detected using minimum and maximum values in a scalable mask. In the second step, a corrupted pixel is corrected using the local correlation between the uncorrupted pixels in the mask. This step specifically performs edge-directed filtering using principal component analysis to preserve the edge and detail information in the highly corrupted image. The experimental results showed that the proposed method can reduce impulse noise significantly and preserve more edge information than the existing state-of-the-art methods. In addition, the proposed method outperforms existing methods for highly corrupted images by an average of 6.47 dB. Therefore, we believe that the proposed method can be a useful tool for removing impulse noise in the field of infrared related devices and digital cameras.

Abstract High performance, full color electrophotographic printers are gaining acceptance in many office environments. In this study, the authors controlled the aggregation of three different colloidal dispersions using four different multivalent metallic coagulants over a wide pH range to develop a polyester-based chemically prepared toner (CPT). An operational limit existed for the total quantity of each metallic coagulant required to achieve a narrow particle size distribution at a mean target aggregate size. This, when exceeded, produced a viscous, inoperative sludge in the reactor. The optimal pH condition for each coagulant system was mainly dependent on the electrostatic balance produced by deprotonation of exposed carboxylic acid groups on the polyester resin particles at a pH between 5.5 and 6.5. Additional electrostatic interactions between the polyester colloidal dispersions and the monovalent cations (M1⁺) in the metallic coagulation system at high electrolyte concentrations created a favorable environment to reproduce core-toner particles with a narrow particle distribution at a mean target size. By manipulating the aggregation process, the individual nano-dispersions coalesced in an aqueous environment to form a polyester-resin-based chemical toner that was uniform in particle size and had low total volatile organic compound (VOC) level. The printing and image performance of this toner using a color laser printing system was also observed. This final polyester toner was optimized for high speed, energy efficient electrophotographic printers that utilize an oil-free fusing subsystem that operates at a low fusing temperature. The image quality and toner usage of these toners meet the specifications of major printer manufacturers for digital printing technologies.