Hierarchical Intra Mode Decision for H.264/AVC

The intra mode prediction via exhaustive mode decision exploited in the H.264/advanced video coding effectively improves the coding efficiency, but at the expense of yielding higher computational complexity. In this letter, a fast intra mode decision algorithm, called the hierarchical intra mode decision (HIMD), is proposed to speed up the mode decision process by reducing the number of modes required to be checked for each macroblock. The novelty of the proposed HIMD algorithm lies at the following accounts. 1) An early decision with adaptive thresholding is developed for the mode decision of the luma component. 2) The candidate modes are selected according to their Hadamard distances and prediction directions. 3) Only one of the hierarchical paths will be chosen to compute its least rate-distortion cost. Experimental results have shown that the proposed HIMD algorithm achieves a reduction of 85.75% computational complexity on average, while incurring only 0.164 dB loss in peak signal-to-noise ratio (PSNR) and 2.336% increment on the total bit rate compared with that of exhaustive mode decision, which is a default approach set in the joint model reference software.