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

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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.

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