SWITCHING POINT ESTIMATION METHOD, RESOLUTION SWITCHING METHOD, IMAGE COMPRESSION METHOD, IMAGE EXPANSION METHOD, AND APPARATUSES THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a compression/expansion method by which a switching point for whether to perform resolution conversion for improving a picture quality can be easily estimated.

SOLUTION: A quantization coefficient Qccorresponding to the switching point is estimated by using a correlative expression which represents the switching point for switching whether to convert the resolution of an image in accordance with the compressibility and quality of an image in relation to the difference PSNRLof picture quality between an image before filter processing and an image after filter processing. Then a quantization coefficient Q for compressing the image into desired compressibility is compared with the estimated quantization coefficient Qc, it is determined whether to convert the resolution of the image in accordance with the comparison result, and image compression is performed. When expanding the image, it is judged whether the resolution has been converted and interpolation is performed in accordance with the judgment result, thereby outputting a restored image.

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