In a digital camera printing system, dynamic range is usually compressed linearly in log-log scale and good image is obtained as a whole. However, the image has a tendency to give us a flat impression without liveliness compared with silver halide photography. So, a sigmoid function is proposed and is applied to tone rescaling. The sigmoid function has the characteristics that the γ value and the position of the steepest point of the curve of the function are adjustable. Several methods of determining the parameters of the sigmoid function are studied. When the steepest point is determined to the peak of the histogram of region of interest and γ value is adjusted to around 1.4, it is confirmed that the image quality is especially improved in subjective estimation.

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The Three-Level highlight color imaging, which is a one-pass process built by combinations of charged and discharged area developments, has a special problem of fringe images. The fringe image is a ghost image of the opposite color toner caused by edge effect which appears at an image edge. In this study, we examined phenomena on the fringe images. And we developed “Edge Effect Control Technology” (EECT) for avoiding fringe images. An auxiliary laser power level is exposed to the area where the fringe image is to be appeared on the photoconductor, and loosen the edge effect by avoiding dramatic potential changes on the photoconductor. Finally, Adequate conditions of EECT is revealed.

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DCT (Discrete Cosine Transform) is very powerful algorithm for image processing and plays essential role in image coding. Security, management by image, and machine vision increase their importance with the progress of computer and CCD camera. This paper proposes a system which automatically detects an object passing through a focused area of the camera by applying DCT and captures an image of the object. 8×8 DCT matrices are arranged as a two-dimensional array on the original image. The magnitude of high frequency components of the DCT matrixes is continuously monitored, and images are captured and stored in memory only when it peaks. The images of the object in focus are only stored, so memory volume can be greatly saved and also it becomes easy to look up the wanted image.

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This paper describes a color management system of reflective-type LCD (R-LCD). Since the R-LCD works together with its ambient light as a light source, it is expected that the colorimetric color on the R-LCD must be changed if the illuminant is changed. As a color management of such R-LCD, we propose a color management system of the R-LCD in terms of adaptation of the Human Visual System to light source variation.
In this research, first, we conducted a subjective experiment to obtain RGB code value that is required in order to display a corresponding color on the R-LCD under varying ambient light condition. The result of the experiment shows that the corresponding color of the experimental results was reasonably approximated by the color obtained by the von Kries model.
Secondly, we proposed a color compensating mechanism that is described as simple 3×4 linear matrix. Then, we described a prototype of the imaging system that equipped with an ambient light sensor, which makes the system possible to change its color depending on an ambient light variation.
Since the sensor sense kinds of ambient lights and built-in circuits generate 3×4 color matrixes automatically, the system can display desired colors for Human Visual System in accordance with an adaptation for ambient lighting. Subjective evaluation under a variety of ambient light sources brought us more favorable result than by a conventional type of R-LCD.

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The shape and driving speed of the spiral screw agitator in a developing unit that has a pair of spiral screw agitators are investigated. In the developing unit, there is a variety of image densities on both edges of the paper caused by varied toner concentration depending on the direction of flow of developer. This is because toner is consumed during the developer conveyance. We analyzed the relationship between the toner concentration and the flow rate of the developer in the channel. We also analyzed the relationship between the flow rate of the developer and the shape and driving conditions of the spiral screw agitator. We were able to achieve a condition in which there is no variation in the image density. The analyzed results were experimentally verified. Using the results, we considered how to design agitator after the printer specifications, i.e. print speed or paper size, were defined.

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We have studied the conditions for eliminating background noise in the two-component conductive magnetic brush development process, both theoretically and experimentally.
A well-known maxim in this field is that a low-charged toner causes background noise. To confirm this maxim experimentally, we studied the relationship between background noise and development parameters, considering the electric and Van der Waals forces on the charged toner.
Our investigation produced the following results. First, extremely small or extremely large toner charges cause background noise, indicating that there is an optimum range for toner charge. Second, increasing the capacity of the photoconductor or decreasing the size of the toner particles expands the optimum range. The theoretical expression obtained agrees relatively well with the experimental data. Based on this expression, the suitable parameter values necessary for eliminating background noise and the required optical density were elucidated. These values included photoconductor capacity, reverse bias developing voltage, size of toner particles, and toner charge to mass ratio.

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JPEG2000, a new still image compression standard, was approved by ISO in 2001. Because JPEG2000 is based on DWT (Discrete Wavelet Transform), block noises are greatly reduced, but the problem of mosquito noise is left unsolved. This paper proposes an algorithm which reduces the mosquito noises of JPEG2000 decoded images by using ε-filter. The variance values of brightness levels of picture elements within each block are calculated for every picture elements in an image, and the maximum value among them are used for the ε-filtering. Subjective image evaluation results show that the proposed algorithm can largely improve the image quality.

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