In order to reach higher coding efficiency compared to its predecessor, a state-of-the-art video compression standard, the High Efficiency Video Coding (HEVC), has been designed to rely on many improved coding tools and sophisticated techniques. The new features are achieving significant coding efficiency but at the cost of huge implementation complexity. This complexity has increased the HEVC encoders' need for fast algorithms and hardware friendly implementations. In fact, encoders have to perform the different encoding decisions, overcoming the real-time encoding constraint while taking care of coding efficiency. In this sense, in order to reduce the encoding complexity, HEVC encoders rely on look-ahead mechanisms and pre-processing solutions. In this context, we propose a gradient-based pre-processing stage. We investigate particularly the Prewitt operator used to generate the gradient and we propose necessary approaches that enhance the gradient performance of detecting the HEVC intra modes. We also set different probability scenarios, based on the gradient information, in order to speed up the mode search process. Moreover, we propose a gradient-based estimation of the texture complexity that we use for coding unit decision. Results show that the proposed algorithm achieves a reduction of 42.8% in encoding time with an increase in BD rate of only 1.1%.

Abstract. In order to reach higher coding efficiency, the design of the newest video compression standard -High Efficiency Video Coding (HEVC) -is relying on many improved coding tools and sophisticated techniques. Such a complexity leads to the vital need of video encoders for fast algorithms to overcome the real-time encoding constraint and memory limits. In this context, we propose a gradient based pre-processing stage that will help decreasing the complexity of the encoder and will speed up the Intra mode decision. For that purpose, we investigate the potential of a Prewitt operator instead of the famous Sobel operator used to generate the gradient. In addition and in order to enhance the gradient potential of Intra mode detection without adding a significant complexity, we propose an optimized Intra mode selection through a neighbor mode extension as well as an adapted cost function to take into account the appearing number of modes and the gradient magnitudes. The obtained results demonstrate that we can reduce the encoding time for All Intra configuration by 31.9% with a loss in BD-rate of only 1.1%.