| 摘要 |
PCT No. PCT/FI85/00096 Sec. 371 Date Sep. 28, 1987 Sec. 102(e) Date Sep. 28, 1987 PCT Filed Dec. 5, 1985 PCT Pub. No. WO87/03768 PCT Pub. Date Jun. 18, 1987.The invention relates to a conditional replenishment 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 image into a transmission channel which functions at the rates of narrow bandwidth data connections. The digitized picture information read into the video memory is compared to the already transmitted picture information stored in the reference memory, and the change value (M) between these is compared to the preset change threshold (T). If the change value (M) surpasses the change threshold (T), the picture information of the respective picture area is coded and transmitted, and the corresponding picture information is stored into the reference memory, preparatory to a new comparison. The comparison between the new picture information and the transmitted picture information is carried out so that the change values (M) in each predetermined picture area are calculated by summing, pel by pel, the differences among the new picture and the reference pictures. The change values (M) obtained for each picture area are combined into a change histogram of the whole frame, which histogram contains the change values (M) in order of magnitude. From this change histogram, there is chosen a number defined by a predetermined reference value (Nc) of picture areas with the largest change values (M). The change value (M) of the chosen picture area with the smallest change value (M) is set as the change threshold (T=Mopt). |
