This invention relates to an effective moving image data encoding method under a special dialog environment, in which the moving image data with information being only concentrated in a part of region of display image such as that in a bidirectional dialog system which implements a real-time bidirectional dialog. The said encoding method divides image frame constituting the moving image data into a plurality of rectangular regions, these plurality of rectangular regions, correspond individually to a pre-set ROI and non-ROI. Then, by means of compressing those rectangular regions sequentially in such away that the number of code of the rectangular region which correspond to the ROI is larger than that correspond to the non-ROI, thereby generating the encoding data of individual image frames.
The moving image data encoding and decoding method, and terminal device implementing those methods as well as the bidirectional dialog type system