Abstract: A video bit rate control method. SUBGOPs are defined as sets of two to four frames in a GOP. For example, if the GOP comprises IBBPBBPBBPBB frames, each of the SUBGOPs is defined as a set of the IBBP or BBP frames. Before bit assignment is performed with respect to frames to be coded, it is checked whether a scene change is present with respect to frames in successive ones of the SUBGOPs. If it is checked that the scene change is not present, a bit rate is controlled in a conventional manner. In the case where the scene change is present, a smaller bits than that in the conventional manner is assigned to frames with no scene change and a relatively large bit amount is assigned to a frame with the scene change. Therefore, according to the present invention, the video bit rate control method has the effect of preventing a degradation in a picture quality due to the scene change.

Abstract: An image signal transmitting system uses the difference between image frames, which can transmit lots of information in a small amount of data, by transmitting the acutal moving areas which are extracted by using two change detecting masks and whose contours and textures are encoded for human visual perception. A larger amount of information is expresssed by a smaller amount of data by extracting the motion in a unit of frames, not in a unit of blocks, and expressing a converted portion by its contour and texture to facilitate the recognition of the converted portion.