Electrophotographic Printers Research Articles

Measuring colorant fading within raster regions of printed scanned customer content using a novel unsupervised clustering method

Colorant fading defects in raster region of interest (ROI) are among the most common printing issues in electrophotographic printers. Colorant fading manifests as faint print or customer content and is usually caused by low-level ink/cartridge. This paper presents an accurate method to detect the colorant fading defects and classify the defects based on their severity. There are two modules for this method. The first module uses the SLIC super-pixel method to separate the raster ROI and extract the smooth super-pixels. We design a novel unsupervised clustering algorithm to automatically extract the three or four main colors from the smooth super-pixels. Unsupervised data clustering is an important problem that arises in many image processing applications. We propose a new approach to unsupervised data clustering called Data Inter-Distance MEdiated Clustering (DIDMEC). Our new method is based on analyzing the matrix of Euclidean distances between each pair of points in the data set. Based on three simple properties, we devise an approach that effectively yields the same accuracy as the K-Means algorithm but at a much lower computational cost for a moderate number of sample points. The second module extracts feature vectors for each main color clustered by DIDMEC to classify the colorant fading defects based on their severity.

Measuring margin and skew errors in scanned printed customer content

Print margin and skew describe an image placed crookedly on the printed page. It is one of the most common defects in electrophotographic printers and dramatically affects print quality. It primarily might occur when using a two-sided printing module on the printer. To solve or correct the print margin and skew error, we should first accurately detect the print margin and skew on the printed page. This paper proposes a method to accurately detect the print margin and skew based on the Hough Lines Detection algorithm. There are three steps of this print margin and skew detection method. We first project the digital master images into the scanned test image with master image edges. The second step is the most challenging part of designing this method because all of our scanned test pages had only two or three and barely visible edges of the printed paper to the naked eye. We use an image processing method and Hough Lines Detection algorithm to extract the paper edges. The third step uses the projected master images edge and the extracted paper edges to calculate the print margin and skew result. Our algorithm is an efficient and accurate method to detect print margin and skew errors based on factual scanned image verification.

Streak Detection in Color Printed Customer Content

Streaks are one of the most common print defects in electrophotographic printers that influence print quality. Streak defects are dark or light lines with the major axis along the printing process direction and are usually caused by a defective Intermediate Transfer Belt (ITB) or Organic Photo Conductor (OPC) component in the printer. Previously, we designed an algorithm to detect the streak defects only on standard printed test pages, which have uniform color [1]. In this paper, we design an algorithm to detect the streak defects on the customer content area, which we call a raster ROI. It is more complicated than the uniform color printed page because the customer content influences our streak detection result. Sometimes, the customer content has some dark or light straight lines along the printing process direction, and they are similar to streak defects. To detect the streak defects on the customer pages, we must separate the straight lines of customer content and the streak defects. To detect the streak in a raster ROI, we apply the Sobel edge detection algorithm and morphological operations to the master image, which includes the customer content without defects, to remove the straight customer content lines on the scanned test pages. The remaining dark or light straight line along the printing process direction may be streak defects. For the detected streak defects, we use the DAG-SVM multi-classification method to classify the rank of streak defects in the raster ROI.

Color Text Fading Detection

The text fading defect is one of the most common defects in electrophotographic printers; and it dramatically affects print quality. It usually appears in a significant symbol Region of Interest (ROI), easily noticed by a user on his or her print. We can detect text fading by the density reduction for the black and white printed symbol ROI. It is difficult to detect the color text fading only by density reduction, because the depleted cartridge may only cause the color distortion without density reduction in the color printed symbol ROI. In our previous work with print quality defects analysis, the text fading detection method only works for black text fading defect detection [1]. Our new text fading method can detect the color text fading defect and predict the depleted cartridge. In this new text fading detection method, we use whole page image registration and the median threshold bitmap (MTB) matching method to align the text characters between the master and test symbol ROIs, because with the aligned text characters, it is easy to extract the difference between the master and the test text characters to detect the text fading defect. We use a support vector machine classifier to assign a rank to the overall quality of the printed page. We also use the gap statistic method with the K-means clustering algorithm to extract the different text characters’ different colors to predict the depleted cartridge.

A comprehensive system for analyzing the presence of print quality defects

Print quality (PQ) is most important in the printing industry. It plays a role in users’ satisfaction with their products. Page quality will be degraded when there are print quality defects on the printed page, which could be caused by the electrophotographic printer (EP) process and associated print mechanism. To identify the print quality issue, customers have to consult a printer user manual or contact customer service to describe the problems. In this paper, we propose a comprehensive system to analyze the printed page automatically and extract the important defect features to determine the type and severity of defects on the scanned page. This system incorporates many of our previous works. The input of this system is the master digital image and the scanned image of the printed page. The comprehensive system includes three modules: the region of interest (ROI) extraction module, the scanned image pre-processing module (image alignment and color calibration procedure), and the print defect analysis module (text fading detection, color fading detection, streak detection, and banding detection). This system analyzes the scanned images based on different ROIs, and each ROI will produce a printer defect feature vector. The final output is the whole feature vector including all the ROI feature vectors of the printed page, and this feature vector will be uploaded to customer service to analyze the printer defect.

Cost-function-based repetitive interval estimation method with synthetic missing bands for periodic bands in electrophotographic printer

Cost-function-based repetitive interval estimation method with synthetic missing bands for periodic bands in electrophotographic printer

Monochrome hybrid, multilevel, halftone screen with unequal spatial resolution for a low-cost electrophotographic printer

Monochrome hybrid, multilevel, halftone screen with unequal spatial resolution for a low-cost electrophotographic printer

Visualization Analysis on Melting Deformation of Toner Particles in a Fusing Nip

Image gloss in electrophotographic copiers and printers is closely related to the image structures, which are spatial structures of melted toner layers on media. Therefore, in order to design the image gloss when copiers and printers are developed, it is necessary to clarify relations between the image gloss and the image structures, and relations between the image structures and system parameters. We clarified the relations between the image gloss and the image structures by constructing a relation model between the image gloss and characteristic indices of two image structures that crucially affect the image gloss in our previous report. However, with respect to clarifying the relations between the image structures and the system parameters, analysis on the melting deformation behavior of toner particles is the most important problem to be solved. In this report we newly developed a visualization measurement method for melting deformation of toner particles in a fusing nip. The method enables us to directly observe the behavior of toner particles in the fusing nip under the condition simulating time variation of temperature and pressure in the actual fusing system. By using the method, dependences of the deformation behavior of the toners in the fusing nip on the system parameters were analyzed. As a result, it was found that the toner particles are deformed completely in the fusing nip. We also clarified the effect on the deformation of toner particles in the fusing nip caused by temperature of a heating unit and that of a pressurizing unit. Considering the results, it was found that the restoring deformation of the toner after the fusing nip caused by residual stress stored inside the toner particle significantly affects the image structures and image gloss after fusing.

The Lattice-Based Screen Set: A Square N -Color All-Orders Moiré-Free Screen Set.

Periodic clustered-dot screens are widely used for electrophotographic printers due to their print stability. However, moiré is a ubiquitous problem that arises in color printing due to the beating together of the clustered-dot, periodic halftone patterns that are used to represent different colorants. The traditional solution in the graphic arts and printing industry is to rotate identical square screens to angles that are maximally separated from each other. However, the effectiveness of this approach is limited when printing with more than four colorants, i.e., N -color printing, where N > 4 . Moreover, accurately achieving the angles that have maximum angular separation requires a very high-resolution plate writer, as is used in commercial offset printing. Commercially available high-end digital printers cannot achieve this resolution. In this paper, we propose a systematic way to design color screen sets for periodic, clustered-dot screens that offer more explicit control of the moiré properties of the resulting screens when used in color printing. We develop a principled approach for the moiré-free screen design that is called lattice-based screen design. The basic concept behind our approach is the creation of the screen set on a 2D lattice in the frequency domain, and then picking each fundamental frequency vector of the individual colorant planes in the created spectral lattice according to the desired properties. The lattice-based screen design offers more flexibility in designing N -color screen sets with different halftone geometries, and all of them are guaranteed to be all-orders moiré-free. We demonstrate the efficacy of our proposed method by introducing several new screen designs, and a comparison with published screen designs.

Technology in Contact Roller Charging Device of Electrophotographic Printer

Technology in Contact Roller Charging Device of Electrophotographic Printer

Halftone Blending Between Smooth and Detail Screens to Improve Print Quality With Electrophotographic Printers.

In this paper, we consider a dual-mode process for the electrophotographic laser printer--a low-frequency halftoning for smooth regions and a high-frequency halftoning for detail regions. These regions are described by an object map that is extracted from the page description language version of the document. This manner of switching screens depending on the local content provides a stable halftone without artifacts in smooth areas and preserves the detail rendering in detail or texture areas. However, when switching between halftones with two different frequencies, jaggies may occur along the boundaries between areas halftoned with low- and high-frequency screens. To reduce the jaggies, our screens obey a harmonic relationship. In addition, we implement a blending process based on a transition region. We propose a nonlinear blending process in which at each pixel, we choose the maximum of the two weighted halftones, where the weights vary according to the position in the transition region. Moreover, we describe an online tone-mapping for the boundary blending process, based on an offline calibration procedure that effectively assures the desired tone values within the transition region.

Gloss Prediction Model for Electro-photographic Printing Based on Image Structures Related to Physical Phenomena in the Image Forming Processes

In developing copiers and printers, it is necessary to design the image gloss according to customers' preferences. In electro-photographic printers, the image gloss depends on the system parameters, such as parameter sets for fusing (pressure, temperature, and dwell time), viscoelastic property of toners, and surface properties of paper. Therefore, it is necessary to develop system models that indicate relations between the image gloss and system parameters. In this paper, we describe the development of an image gloss prediction model based on image structures that are related to the physical phenomena in the system. We have extracted two characteristic image structures from the analysis of image samples printed by various system parameters. A “micro hollow at the toner boundary” is a boundary dimple among a few toner particles, and a “macro hollow” is a pit composed of a group of toner particles. The “micro hollow at the toner boundary” is formed by a melting phenomenon of the toner particle in the fusing process, and the “macro hollow” is affected by the arrangement of the toner particles in the pre-fusing process. Furthermore, we succeeded in constructing a model that predicts the image gloss based on the sum of the area ratios (occupancy ratio in the surface area) of the two image structures.

28pm1-F-1 電子写真用機能性ゴムローラの微小すべり量の観察

28pm1-F-1 電子写真用機能性ゴムローラの微小すべり量の観察

Scanned image descreening with image redundancy and adaptive filtering.

Currently, most electrophotographic printers use halftoning technique to print continuous tone images, so scanned images obtained from such hard copies are usually corrupted by screen like artifacts. In this paper, a new model of scanned halftone image is proposed to consider both printing distortions and halftone patterns. Based on this model, an adaptive filtering based descreening method is proposed to recover high quality contone images from the scanned images. Image redundancy based denoising algorithm is first adopted to reduce printing noise and attenuate distortions. Then, screen frequency of the scanned image and local gradient features are used for adaptive filtering. Basic contone estimate is obtained by filtering the denoised scanned image with an anisotropic Gaussian kernel, whose parameters are automatically adjusted with the screen frequency and local gradient information. Finally, an edge-preserving filter is used to further enhance the sharpness of edges to recover a high quality contone image. Experiments on real scanned images demonstrate that the proposed method can recover high quality contone images from the scanned images. Compared with the state-of-the-art methods, the proposed method produces very sharp edges and much cleaner smooth regions.

B-2-4 画像形成装置における光学系を含む駆動・構造連成解析技術の開発

In Electrophotographic copiers and printers, for high image quality it is important to reduce vibration which affects optical systems. To confirm the effect of vibration reduction measures without trial machines, we have developed a numerical analysis method which is coupled mechanism analysis, structural analysis and ray tracing analysis. Using this method, it has become possible to evaluate numerically the dynamic behavior of misregistrations caused by optical parts vibration by vibromotive forces in drive systems and vibration characteristics of main frame, several units and another parts. Experiments for validation of the analysis method also have been done and it is confirmed that the estimated amount of misregistrations were almost the same as that of the experimental results.

An Evaluation Method for Microgloss Uniformity

Microgloss uniformity affects the final image quality of electrophotographic printers. The microgloss is the noise of the micro-gloss differential, and occurs because of either insufficient pressure or toner blistering. Microgloss uniformity evaluation methods have been proposed previously. However, these methods have not been used to establish a standard method. The purpose of this paper is to establish a simple quantitative microgloss evaluation method. The measurement device is composed of a charge-coupled device (CCD) camera and vertically-incident lighting equipment. Because the measurement geometry is 0°/0°, the measuring device is small in size and the camera angle adjustment process is simple. In addition, polarizing filters are inserted into the optical path to suppress any internal diffuse reflected light. The RGB (red-green-blue) image measured by the CCD camera is converted into an L*a*b* image. The L* image is then Fourier transformed to obtain the Wiener spectrum. An evaluation model using Hunter whiteness, a visual characteristic, and the Wiener spectrum was proposed. As a result, the contribution of the evaluation model and the subjective score was 0.94. Because this method is simple, it is expected to find widespread application in the printing industry.

C-1-3 高速カラー電子写真プリンターにおけるトナー画像と記録紙の高精度位置合わせ制御系の開発

C-1-3 高速カラー電子写真プリンターにおけるトナー画像と記録紙の高精度位置合わせ制御系の開発

An Analysis of Moisture Transportation within Paper in the Fusing Process of Electrophotography

Paper curl causes paper jam or print quality degradation in electrophotographic printers and copiers. It is useful to predict amount of the paper curl in electrophotographic process for the efficient products development. The fusing process which is a sub-process of electrophotography is one of the causes of the paper curl. But it had been unclear how the paper curl was generated in the fusing process. In a previous study, a paper curl mechanism based on temperature gradient in paper heating was revealed. The mechanism shows that a temperature gradient causes moisture transfer from the high-temperature side to the low-temperature side within paper and consequently the moisture content of the low-temperature side becomes higher than that of the high-temperature side. This causes a shrinkage difference between both sides of the paper and thus the paper curl is generated. In this report, a one dimensional numerical model to simulate moisture transfer within paper is proposed. In this model, paper is treated as a uniform porous material and the moisture diffusion and transfer are treated according to Darcy's law, as well as evaporation during heating. The computer simulations are carried out to determine the moisture distribution within the paper when the surfaces are heated at different temperatures. The results are finally verified by measuring electrical resistance of papers. They are found to be in good agreement.

New Technology for Improving Image Density Uniformity in the Electrophotographic Process

This paper introduces a new method to reduce periodic density unevenness caused by eccentric rotation of the photoconductor drum and development roller in an electrophotographic printer. In a previous study, a method for controlling periodic density unevenness by using developing bias was proposed. The developing bias is controlled periodically to correct density unevenness. However, no control effects are obtained in low density images; rather, the control somewhat increases the density unevenness.In this study, we developed a new method that reduces the periodic density unevenness through modulation of both charging bias and developing bias based on the rotational periods of the photoconductor drum and development roller. Each bias is periodically changed such that the changes in the developing field due to the eccentric rotation of the photoconductor drum and development roller are cancelled, thus suppressing the periodic density unevenness. Experiments we conducted confirmed that the new method improves periodic density uniformity better than the previous method. The new method guarantees density uniformity is obtained without the use of high-precision components.

C-1-6 高速カラー電子写真プリンターにおける中間転写ベルト制御系の開発(情報・精密機器のサーポ・スマート制御,口頭発表)

C-1-6 高速カラー電子写真プリンターにおける中間転写ベルト制御系の開発(情報・精密機器のサーポ・スマート制御,口頭発表)