H.264/AVC estimates the prediction mode from the modes of neighboring blocks in order to reduce the quantity of bits needed to represent the best mode. The estimated mode is known as Most Probable Mode (MPM). When QP changes, the probability of MPM increases. In this paper, we propose an adaptive mode signaling method based on the probability of MPM. According to the probability of MPM, a conventional MPM method and the proposed merging method are adaptively used to signal the intra prediction mode. Experimental results show that the proposed method achieves an average bit savings of 0.727% and an average PSNR gain of 0.041dB. In the low bit rate condition, the proposed method achieves an average bit savings of 1.795%, and a PSNR gain of 0.103dB, compared to H.264/AVC.

In order to reduce spatial redundancies, the H.264/AVC Intra coding provides nine directional prediction modes including DC prediction for every 44 block, but it needs a lot of overhead bits to represent the nine directional prediction modes for every 44 block. To compress the directional mode bits efficiently, the most probable mode is estimated by using the correlation between the prediction mode of spatially adjacent blocks and that of the current block. In this paper, a new method for estimating the most probable mode is proposed by using the directional information of the prediction mode of the adjacent blocks. Experimental results show that the proposed method is able to achieve a coding gain of about 0.2 dB on average at low bit rate.