IMAGE ENCODING METHOD, IMAGE DECODING METHOD, IMAGE ENCODER AND IMAGE DECODER

摘要

PROBLEM TO BE SOLVED: To encode an image signal with excellent quality by deciding an adjacent block to predict a low-order coefficient value of an encoding object block based on the difference between corresponding low-order coefficient values of adjacent blocks in the case of predicting a low-order coefficient value from a low-degree coefficient among orthogonal transformation coefficients. SOLUTION: An encoding object image 1 is input to a rectangular block division section 2, where the image 1 is divided into uniform rectangular blocks. A block unit encoding object image 3 is input to an orthogonal transformation section 4, in which the image 3 is encoded by DCT or the like, and the pixel value is converted into the frequency domain. A low-order coefficient 6 among conversion coefficients obtained by the DCT is quantized by a quantization section 5 and given to an adaptive low-order coefficient predict section 9 along with a low-order coefficient value 8 of an adjacent block stored in a low-order coefficient value memory 7, in which adaptive low-order prediction is conducted. After a block being an object of low-order coefficient prediction is decided, a difference between a difference between a low-order coefficient of a block and a low-order coefficient of the coding object block is obtained and outputted as a low-order coefficient difference 10.