Kimihiko Kazui

An improved hypothetical reference decoder for HEVC

Hypothetical Reference Decoder is a hypothetical decoder model that specifies constraints on the variability of conforming network abstraction layer unit streams or conforming byte streams that an encoding process may produce. High Efficiency Video Coding (HEVC) builds upon and improves the design of the generalized hypothetical reference decoder of H.264/ AVC. This paper describes some of the main improvements of hypothetical reference decoder of HEVC.

High-Performance Video Codec for Super Hi-Vision

To help pave the way for Super Hi-Vision (SHV) broadcasting, we have developed a new codec system that can encode and decode SHV signals in real time. This is the third generation of SHV real-time hardware codec. This efficient compression system maintains high picture quality by using eight 1080/60p (60 frames/s) encoding units and a video format converter with signal compensation processing that takes the properties of the Dual Green format of SHV into account. The video format converter divides an SHV image spatially into eight 1920 × 1080 portions, each of which is fed to the encoding unit. In the previous SHV codec, the SHV image was divided into 16 portions (spatially eight and temporally two) and 16 1080/30p encoding units were used. Compared with the previous system, the new codec achieves a 50% bitrate saving and downsizes the codec by almost half. Furthermore, several new technologies were developed and installed in the codec. We conducted the worlds first SHV international transmission over an advanced Internet connection using the codec at a TS rate of 260 Mb/s. The received picture quality was good enough to show any kind of SHV content on a large screen.

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.