We present two new techniques for reducing blocking artifacts in motion compensated frames. These techniques can be applied generally to motion compensated frames obtained by employing any partitioning schemes. In the first technique, the weighting coefficients of the overlapped block motion compensation are modeled with fuzzy relations. These fuzzy relations are formed based on two fuzzy sets, which define the closeness of a given pixel to the block boundaries in the horizontal and vertical directions, respectively. The second technique uses the similarity between a set of pixels inside a partitioned region and that on the borders to modify the border pixels. Simulations conducted on several benchmark video sequences indicate that the proposed techniques can improve the subjective quality of the frames as well as reduce the prediction error.
A fast two-stage scheme for the search of the motion vectors under varying interframe brightness characteristics, referred to as enhanced motion vectors, is devised. In the first stage of the scheme, a given block and the corresponding blocks in the search window are mapped into the sum-of-pixel value domain, where two subsets of candidate blocks, one consisting the blocks having the DC values closest to the DC value of the block of interest and the other consisting of those having the farthest DC values are selected. In the second stage, the motion vector is determined by employing these subsets and using the mean square error as the matching criterion. Experimental results show that the proposed technique provides a high prediction accuracy with a low computational load.
Despite the fact that the existing region-wise motion compensation techniques (RWMC) are more efficient than the conventional variable size block motion compensation technique, they still do not use the visual characteristic of a frame in terms of brightness, contrast and sharpness in order to determine the motion information of the partitioned regions in a most efficient manner. The objective of this paper is to present a quad-tree structured region-wise motion compensation technique using enhanced motion vectors. The scheme described in this paper uses the brightness information of a frame in order to reach the objective of having motion vectors with a higher accuracy. Even though using enhanced motion vectors reduces the distortion, it causes the bit rate to increase. This poses the challenge of optimizing the bit rate-distortion performance. The proposed method partitions a frame based on a fine to coarse resolution strategy through the merging and combining processes. The merging process permits 4-to-1, 3-to-1 and 2-to-1 merges. For such merges, the main idea is to minimize the distortion subject to the constraint that the bit rate should not exceed a pre-defined value. The combining process further reduces the total number of partitioned regions by combining some of the regions that have the same enhanced motion vectors. The proposed technique uses a 2-bit code for coding the quad-tree structure while two different code lengths encode the enhanced motion vectors of the partitioned regions depending on the differential brightness threshold value. The proposed method is applied to a number of video sequences and compared with the other existing methods. The test results show that the new method can significantly improve the rate-distortion performance.