基于宏块预判的快速帧内预测模式选择算法

Fast Intra Prediction Mode Selection Algorithm Based on Macroblock Judgement

针对H.264/AVC帧内预测模式选择部分计算复杂度问题,提出一种基于宏块预判的快速帧内预测模式选择组合算法.该算法采用低复杂度的三点梯度算子改进了边缘方向直方图帧内预测模式选择算法(Pan算法)中利用Sobel算子得到边缘方向矢量.首先运用平均绝对误差(Mean Absolute Difference,MAD)值对编码宏块类型结合QP下的阈值进行预判;预判后的宏块采用改进的Pan算法进行模式筛选,最后确定最佳的预测模式.实验结果表明,在6个不同视频序列全I帧编码情况下,该算法与全搜索算法相比编码时间平均减少大约72.4%,与Pan算法相比编码时间减少28.6%,而码率仅分别增加4.21%、1.8%,峰值信噪比基本不变.

To simplify the computational complexity of intra prediction mode selection for H.264/AVC, a fast intra prediction mode selection combination algorithm based on macroblock judgment is proposed in this study. This algorithm uses the three points gradient operator with a low-complexity to improve the edge direction histogram intra prediction mode selection algorithm （Pan algorithm）, which obtains edge orientation vector by Sobel operator. Firstly, the MAD （Mean Absolute Difference） value is used to predict the threshold of the encoded macroblock type combined with QP. Then, the improved Pan algorithm is used to filter the pre-determined macroblock. Finally, an optimal prediction mode can be determined. The experimental results show that under the condition of six video sequences with all-I-frame coding, this algorithm reduces the coding time by about 72.4%. Compared with the Pan algorithm, the coding time is reduced by 28.6%, while the bit rate is increased by 4.21% and 1.8% respectively, and the PSNR is invariable.