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:
“Get behind me, Satan! You are a stumbling block to me; for you are setting your mind not on divine things but on human things.”
—Bible: New Testament, Matthew 16:23.
Jesus to Peter.
“The motion picture is like a picture of a lady in a half- piece bathing suit. If she wore a few more clothes, you might be intrigued. If she wore no clothes at all, you might be shocked. But the way it is, you are occupied with noticing that her knees are too bony and that her toenails are too large. The modern film tries too hard to be real. Its techniques of illusion are so perfect that it requires no contribution from the audience but a mouthful of popcorn.”
—Raymond Chandler (1888–1959)
“... the compensation for a death sentence is knowledge of the exact hour when one is to die. A great luxury, but one that is well earned.”
—Vladimir Nabokov (1899–1977)