METHOD FOR COMPANDING IMAGE CHARACTER DATA, SYSTEM THEREFOR AND INFORMATION RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To reduce a mosquito noise, to attain processing of large-scale image- character data at a high speed, to obtain high image quality and to decrease the scale of a device. SOLUTION: Companding processing is applied to a large-scale image and character data without having to distinguish them. A character-simple image detection section 1 recognizes it to be a character-simple image when 'an arbitrary number being 2 or over' with different gradation levels with respect to the processing unit of discrete cosine transform processing for compression luminance processing in the joint photographic experts group JPEG/ITU-T Standards. A JPEG compressor 2 applies quantization processing to low frequency components and high frequency components data, by revising the value of a quantization table so that data converted of both by the discrete cosine transform processing are not missing corresponding to this recognition. Then a JPEG expansion device 3 processes the high frequency components, by revising the contents of the quantization table to be the same as the case with the compression processing in the case of inverse-quantizaion, when the compressed image data are character-simple image data, expands the image data of the frequency components and provides an output.