Method for fast bits estimation in rate distortion for intra coding units in HEVC

Improved performance of Intra Prediction in HEVC in comparison to H.264/AVC is primarily due to two main feature enhancements, first is increase in the number of intra prediction directions and secondly due to the support for larger transform sizes. Using lagrangian based rate distortion measure to decide the appropriate prediction direction and Transform Unit size requires calculation of bits generated using complete cabac encoding for every candidate, which is computationally very exhaustive. In order to avoid complex cabac encoding is to use only distortion as a comparison measure, but it has a detrimental effect on coding efficiency. In this paper we present a method based on regression, to estimate the cabac bits for direction mode and for Transform Unit based on the magnitude of non-zero coefficients. This way we avoid calculating cabac encoding for bits calculation and the results show that our method gives 5.4% average BD-rate gain for Luma in comparison to using only distortion as a comparative measure.