A Study on a New Principle of Image Compression

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Main results obtained in the research are listed below.(i) A new image generation model, Modified AR model, was developed to approximate the amplitude characteristic of real image signals well.(ii) Conventional coding schemes such as DCT,DPCM,and fractal coding show almost the same compression performance to pseudo-image signals generated by using (i) as to the real image signals.(iii) A spectrum exchange method to generate hybrid image signals was proposed, where amplitude spectrum or phase spectrum of the real image signal is exchanged to that of the pseudo-image signal.(iv) Compression experiment of a variety of hybrid image signals generated with the technique of (iii) shows that only the information of the amplitude spectrum is used and phase information is not used for compression by DCT,DPCM,and fractal coding.(v) It is made clear that shape information which characterizes an image is included in the phase spectrum that is not used in conventional coding schemes.(vi) It is strongly desired to introduce a direct use of the phase information, that is, shape information into image compression schemes.(vii) As one of the image compression schemes to use shape information directly, a new, variable shape fractal coding scheme that integrates small basic blocks to form a range block adjusted to the shape was proposed.(viii) The above scheme achieves the improvement of compression performance by approximating the shape more efficiently and accurately.(ix) As the second scheme that uses the shape information effectively, an arbitrary shape DCT scheme is proposed.(x) A great improvement of compression performance is obtained by the DCT-based arbitrary shape coding scheme.