Overlapped block motion compensation (OBMC) is a good solution to these problems because it not only increases prediction accuracy but also avoids blocking artifacts. When using OBMC, blocks are typically twice as big in each dimension and overlap quadrant-wise with all 8 neighbouring blocks. Thus, each pixel belongs to 4 blocks. In such a scheme, there are 4 predictions for each pixel which are summed up to a weighted mean. For this purpose, blocks are associated with a window function that has the property that the sum of 4 overlapped windows is equal to 1 everywhere.
Studies of methods for reducing the complexity of OBMC have shown that the contribution to the window function is smallest for the diagonally-adjacent block. Reducing the weight for this contribution to zero and increasing the other weights by an equal amount leads to a substantial reduction in complexity without a large penalty in quality. In such a scheme, each pixel then belongs to 3 blocks rather than 4, and rather than using 8 neighboring blocks, only 4 are used for each block to be compensated. Such a scheme is found in the H.263 Annex F Advanced Prediction mode
Read more about this topic: Motion Compensation
Famous quotes containing the words block, motion and/or compensation:
“It is, in both cases, that a spiritual life has been imparted to nature; that the solid seeming block of matter has been pervaded and dissolved by a thought; that this feeble human being has penetrated the vast masses of nature with an informing soul, and recognised itself in their harmony, that is, seized their law. In physics, when this is attained, the memory disburthens itself of its cumbrous catalogues of particulars, and carries centuries of observation in a single formula.”
—Ralph Waldo Emerson (1803–1882)
“Too many Broadway actors in motion pictures lost their grip on success—had a feeling that none of it had ever happened on that sun-drenched coast, that the coast itself did not exist, there was no California. It had dropped away like a hasty dream and nothing could ever have been like the things they thought they remembered.”
—Mae West (1892–1980)
“I have everything in the world that is necessary to happiness, good faith, good friends and all the work I can possibly do. I think God’s greatest blessing to the human race was when He sent man forth into the world to earn his bread by the sweat of his face. I believe in toil, in the dignity of labor, but I also believe in adequate compensation for that toil.”
—Anna Howard Shaw (1847–1919)