Improvement of picture quality and coding efficiency using discrete cosine transform
Yuuji Izawa, Masaaki Takizawa · Electronics and Communications in Japan (Part I Communications) · 1990
Abstract In the applications of still picture coding such as image data base, the progressive coding is effective in reducing the retrieval time and the transmission cost. For the block coding based on the discrete‐cosine transform (DCT), a study has been made on the progressive and successive transmission from dc to higher‐order ac components. In this scheme, the major cause of the picture quality degradation is the block distortion produced at the initial stage. This paper proposes two methods to reduce the block distortion where the lower‐order ac coefficients are determined from the dc coefficients transmitted at the first stage and applied the inverse‐DCT. The first method is to determine the lower‐order ac coefficients so that pixel values are smoothly connected at some points on the block boundary. The second method is based on the application of the interpolation filter utilizing the property of DCT. Furthermore, it is shown that by transmitting the difference between the DCT coefficients to be transmitted and the coefficients generated by the proposed method, the coding efficiency can be improved by 5 to 8 percent.