IMAGE CODING METHOD AND IMAGE DECODING METHOD

摘要

An image decoding method that is capable of alleviating declines in coding efficiency and subjective image quality, selects, by switching types of inverse orthogonal conversion according to a coded image, an inverse orthogonal conversion, between a first and a second inverse orthogonal conversion (S20), which is applied to the coded image; inverse quantizes the coded image (S21); carries out the inverse orthogonal conversion, selected by the switching, upon the inverse quantized coded image (S22); and generates a decoded image by adding a differential image generated by the inverse orthogonal conversion and a predict image corresponding to the coded image (S23). The subjective image quality of the decoded image generated using the first inverse orthogonal conversion is greater than the subjective image quality of the decoded image generated using the second inverse orthogonal conversion, and the second inverse orthogonal conversion has a higher conversion efficiency than the first inverse orthogonal conversion.