Fast variable-size block motion estimation using merging procedure with an adaptive threshold

A merging procedure for variable-size block motion estimation is proposed to reduce the computation for block-size decision. A smaller block-size is initially used for motion estimation. An adaptive threshold, which depends on the information obtained from the motion estimation, quantization parameter, and rate distortion cost function is used to determine if the motion vectors of the neighboring blocks should be merged or not. We simulate the proposed merging procedure using an H.264 video encoder to determine if 16x16, 16x8, 8x16, or 8x8 blocksize should be used for each macroblock. Based on the simulations, performance of the proposed method is close to that of H.264 JM2.1 when 16x16, 16x8, 8x16 and 8x8 block modes are enabled and the exhaustive search method is used to determine the block-sizes. Computational complexity can be significantly reduced by the proposed algorithm since it only performs the motion search for one block-size.