JPEG (Joint Photographic Experts Group) baseline algorithm is widely used because of its high compression capability. The algorithm has characteristics that the degradation of image quality becomes to be perceived as compression ratio becomes high. The eyesore degradations are false contour and mosquito noise. The new method of improving the image quality is proposed. The first step: false contour areas are extracted from image and the second step: the areas are smoothed by fitting process. It is confirmed that this method is effective in improving the image quality degraded by JPEG high compression.
An electrical simulation program of 2-dimensional charging roller system is developed in order to make clear the discharge phenomena and charging property of the roller. The Poisson equation of electrostatic field and the Ohm law are solved using the finite difference method on the boundary-fitted coordinate system, and the amount of charge deposited on the photoconductor is estimated from the Paschen law. The numerical results show good agreement with the theoretical and the experimental results. In case of low resistive roller biased DC voltage, discharge happens only in the entrance of the nip between the roller and photoconductor. On the other hand, in case of resistive roller biased DC voltage, discharge happens in not only the entrance but also the exit of the nip.
Xerographic prints have a peculiar surface structure different from that of lithographic prints, mainly due to extensive use of uncoated, mat paper and a relatively high density of toner. Since the color toners usually form glossy images to secure color saturation, the non-image area and the image area largely differ in the level of gloss. Thus, any toner distribution always accompanies a corresponding gloss distribution, and any disturbance in toner image yields not only density noise but also gloss fluctuation. We covered a full color image with a uniform layer of clear toner with the intention of reducing such gloss fluctuation. The results were a much more uniform gloss and a remarkable reduction of noise. Microscopic observations of image structure, a colorimetric dot gain analysis and gloss fluctuation measurement using polarized light showed that noise reduction was caused by not only the decrease of gloss fluctuation due to image surface flattening, but the prevention of image disturbance during fusing.