Intra-Prediction Mode Decision Algorithm Based on Orientation Gradient for H.264

Abstract

The rate distortion optimization(RDO) technique employed in H.264 improves coding performance significantly,but a very high computational load is introduced because under full search fashion every macroblock needs calculate R-D costs for all the prediction modes.In this paper,a fast intra-prediction mode decision algorithm based on orientation gradient is proposed to reduce R-D cost calculation.In the proposed algorithm,the gradients between the reference pixels and the current block pixels are calculated in all the prediction directions to detect texture direction and edge strength,and then the prediction modes with larger gradients are prepruned in the prediction process to accelerate encoding.And further,utilizing the spatial correlation of the prediction mode an improved algorithm is presented which adopts most probable mode(MPM) as the default candidate mode instead of direct current(DC) mode.Experimental results for 10 standard sequences demonstrate that compared with JM18.0 full search fashion both the baseline and the improved algorithms employed in luma component intra prediction save more than 50% of the encoding time with a negligible coding performance loss.Keeping the same peak signal-to-noise(PSNR) as JM full search,the baseline algorithm has a bit rate increment of 2.361% and the improved algorithm has a bit rate increment of 1.47% averagely.