Research On Fast Decision Algorithm Of H.264/AVC Intra-mode

H.264/AVC is a new generation video encoding standard developed by VCEG of ITU-T and MPEG of ISO. Because of its higher compression efficiency compared with other encoding standards and good network compatibility, H.264/AVC is widely used in the field of Internet and video communication. However, due to its new encoding technologies to get higher compression efficiency, the complexity of H.264/AVC is almost 10 times of other standards. Power consumption and time delay caused by the complexity make it difficult to exert its superiority in real-time system and resource-constrained embedded devics. Therefore, the coding algorithm must be optimized to ensure the quality of the image and improve the coding speed. Optimizing the coding algorithm to improve the coding speed and ensure the quality of the image has been the hot research topic since the advent of H.264/AVC.By means of analyzing the coding complexity introduced by each key technology, this thesis chooses to optimize the intra prediction mode decision algorithm involved in process of intra prediction and inter prediction. We research a fast intra mode decision algorithm based on the threshold of high frequency component of DCT. In this algorithm,we determine the flat degree of each 8×8 sub-block in 16′16 macroblock by comparing the number of zeros of quantized DCT coefficients with the threshold,and choose appropriate intra coding type for a macroblock according to the quantity of flat 8×8 sub-block. Due to the inevitable errors of quantization and threshold setting, the computation of best prediction modes of all 4×4 sub-blocks is determined by the flat degree of each 8×8 sub-block in Intra 4×4 coding process, so as to make up for the time loss caused by the misjudgment. In the process of intra 4×4 mode decision, the first five modes which are more effective and used more frequently are computed and sorted, then an alternative mode is determined by spatial correlation between prediction modes and textural properties of image for secondary judgement to reduce the range of mode decision.The algorithm is implemented by C programing language in the JM calibration model. By testing different video sequences,coding type decision algorithm without RDO cost calculation can correctly selected more than ~80% macroblock fitting for Intra16′16. Compared to the full search algorithm, our fast intra mode decision algorithm can reduce 30% to 50% encoding time with ~0.04 d B decrement in Peak Signal-to-Noise Ratio(PSNR), and ~5.1% increment in output bit rate and without significant defference in image quality of. In addition,the process of optimization only adds with the fast DCT transform of H.264/AVC itself,in which all operations can be completed only by simple integer addition and shift which is particularly suitable for the embedded devices without floating point sperations and has a certain improvment on the coding speed of real-time system such as video conference and security monitoring system.