# Overlapped Block Motion Compensation

### current pixel vectors frame

**Definition:** The overlapped block motion compensation (OBMC) aims at reducing the blocking effects by performing a weighted average of overlapped block segments during motion prediction.

In normal motion compensation, the current block is composed of 1) the predicted block from the previous frame (referenced by the motion vectors); and 2) the residual data transmitted in the bit stream for the current block. In OBMC, the prediction is a weighted sum of *three* predictions.

Let *(m, n)* be the column & row indices of an 8×8 pixel block in a frame; *(i, j)* be the column & row indices of a pixel within an 8×8 block; and *(x, y)* be the column & row indices of a pixel within the entire frame so that *(x, y) = (m×8* + *i, n×8* + *j* ). Then the weighted prediction for the current block is given by:

(MV° X , MV° y ) denotes the motion vectors of the current block, (MV 1 x, *MV 1 y)* denotes the motion vectors for the block above (below) if the current pixel is in the top (bottom) half of the current block, and (MV 2 x, MV 2 y ) denotes the motion vectors for the block to the left (right) if the current pixel is in the left (right) half of the current block (as illustrated in Figure 1).

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