Tsutomu Shohdohji

Optimization of quantization table based on visual characteristics in DCT image coding

Abstract The DCT (Discrete Cosine Transform) based coding process of full color images is standardized by the JPEG (Joint Photographic Expert Group). The JPEG method is applied widely, for example a color facsimile. The quantization table in the JPEG coding influences image quality. However, detailed research is not accomplished sufficiently about a quantization table. Therefore, we study the relations between quantization table and image quality. We examine first the influence to image quality given by quantization table. Quantization table is grouped into four bands by frequency. When each value of bands is changed, the merit and demerit of color image are examined. At the present time, we analyze the deterioration component of a color image. We study the relationship between the quantization table and the restoration image. Color image is composed of continuoustone level and we evaluate the deterioration component visually. We also analyze it numerically. An analysis method using the 2-D FFT (Fast Fourier Transform) can catch a change of a color image data by a quantization table change. On the basis of these results, we propose a quantization table using Fibonacci numbers.

Optimization of image quality for decoded images using three-dimensional smoothing method

Joint Photographic Experts Group (JPEG) baseline algorithm is widely used because of its high compression capability. The algorithm has a characteristic that the degradation of image quality tends to be perceived as the compression ratio becomes high. The eyesore degradations are false contour and mosquito. A method of improving the image quality is proposed. The first step: a domain of false contours is extracted from the image and the second step: the domain is smoothed by a fitting process. It is confirmed that this method is effective in improving the image quality degraded by the JPEG high compression.

Formation and evaluation of images obtained by the toner jet printing technology (III)

Various nonimpact printing methods used printers are in general use. We have investigated an imaging method using the Toner Jet in which a visible direct image is obtained using an electrostatic field to make the toner stick to the paper. Images obtained from the Toner Jet are of equal quality to those obtained by an electrophotographic method. We have confirmed that the Toner Jet method will be an effective nonimpact printing method in the near future.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Numerical simulation of toner jet method for nonimpact printing

The toner jet method has been previously proposed to perform electrophotographic nonimpact printing easily. To clarify the fundamental properties of this method, the jet behavior of toner is studied through simulation on a personal computer. The mesh electrode is assumed to be inserted halfway between the development roller and the paper-back electrode. This is done to control the locus and the distribution path of toner from the magnetic development roller electrode to the electrode on the back of the paper receiver. The electric field applied between the magnetic development roller and the paper-back electrode is higher than the field between the mesh electrode and the magnetic development roller. The locus and the distribution of toner particles developed on the paper are simulated by changing the applied voltage in each row and each column of the mesh electrode. It is assumed that the jet behavior of toner particles from the magnetic development roller to paper is controllable. In conclusion, the useful role of the mesh electrode in the image quality of the toner jet method is suggested.

Formation and evaluation of image obtained by the toner-jet printing technology

Various nonimpact printing methods used printers are in general use. We have investigated an imaging method using the Toner Jet in which a visible direct image is obtained using an electrostatic field to make the toner stick to the paper. Images obtained from the Toner Jet are of equal quality to those obtained by an electrophotographic method. We have confirmed that the Toner Jet method will be an effective nonimpact printing method in the near future.

Optimization of quantization table in discrete cosine transform (DCT) image coding for color facsimile

The DCT based coding process of full-color image is standardized by the JPEG. The JPEG method is applied widely, for example a color facsimile. The quantization table in the JPEG coding influences image quality. However, detailed research on quantization tables is not sufficiently available. Therefore we study the relations between the quantization table and image quality. We examine first the influence of image quality given by the quantization table. The quantization table is grouped as 4 bands by frequency. When each value of bands is changed, the merit and demerit of color image are examined. At the present time, we analyze the deterioration component of a color image. We study the relationship between the quantization table and the restoration image. Color image is composed of continuous-tone level and we evaluate the deterioration component visually and numerically. An analysis method using the 2-D FFT can catch a change of a color image data by a quantization table change. On the basis of these results, we suggest roughly an optimal quantization table coefficient distribution.