| 摘要 |
Method and apparatus for detecting the most powerfully changed and for the human eye most important picture areas in a video image in order to compress the live image into a transmission channel which functions at the rates of narrow bandwidth data connections. In the conditional replenishment method, the new digitized picture information read into the video memory is compared to the already transmitted picture information stored in the reference memory, and the difference value, i.e. the change value (M) between these is compared to the preset change treshold (T). If the change value surpasses the change threshold (T), the picture information of the picture element (pel) and/or area of image in question is coded and transmitted, and the corresponding picture information is stored into the reference memory preparatory to a new comparison. In the method and apparatus of the invention, the comparison between the new picture information and the transmitted picture information is carried out so that the change values in each predetermined picture area are calculated by means of summing the differences of the intensity readings of the new picture and the reference picture pel by pel, whereafter the change values (M) obtained for each picture area are combined into a change histogram for the whole frame, the said histogram containing the change values (M) of the picture areas in order of magnitude. From the change histogram, there is chosen a number, defined by the predetermined reference value (Nc), of picture areas with the largest change values, and the change value of the chosen picture area with the smallest change value is set as the change threshold (T = Mopt). |
