Akihiro Yamori

Coefficient sign bit compression in video coding

We propose a novel compression technique on signs of DCT coefficients. The proposed technique utilizes a high correlation among pixels at boundaries of a current block and those of neighboring blocks and estimates the original signs. It encodes the difference between the original coefficient signs and the estimated signs. We also propose a speeding up technique for the estimation, utilizing concepts of Gray code and transform matrix decomposition. Compared to JM16.2, the proposed technique reduces 10% bitrate in sign bits of DCT coefficients and achieves 1% BD-bitrate reduction in total bitstream. With the speeding up technique, complexities increase only 8% and 5% on an encoder and a decoder side, respectively.

Enhancement on the motion vector derivation of HEVC for interlace format

We propose a derivation scheme of a motion vector for interlace format. The adjustment of the vertical component of a chroma MV for 4:2:0 format and the adjustment of the vertical component of a luma prediction MV are introduced in order to remove inconsistency between the current derivation process of motion vector predictor and the nature of interlace format in HM4.0. The proposed scheme achieves up to 1.0dB PSNR improvements in chroma components and up to 3.4% bit-rate reduction.