Tomonobu Yoshino

No reference video quality assessment based on parametric analysis of HEVC bitstream

The quality of experience (QoE) on consumer video services must be maintained at a sufficient level. In order to realize automatic quality monitoring with a low burden, a no-reference (NR) objective video-quality-model by using a bitstream is promising because it can estimate a perceptual picture quality by referring to only parameters in the bitstream. High efficiency video coding (HEVC) is expected as the next-generation representative codec. Although parametric NR methods for AVC have been studied, such methods for HEVC are an emerging task in this research field. We propose an objective perceptual video-quality-measurement for HEVC that conforms to the parametric NR scheme.

Low-complexity scheme for adaptive interpolation filter based on amplitude characteristic analysis

Motion-compensated (MC) prediction is one of the most effective coding tools for high-compression video coding. In former works, adaptive interpolation filter (AIF) technology, which improves the coding performance of the fractional-pel MC, has been proposed. As for the real-time codec system, the implementation of AIF based on the Wiener filter algorithm is difficult because of its high computational complexity. To overcome this problem, in this paper, we propose a low-complexity AIF scheme, which can maintain the coding performance achieved by the conventional AIF. The key technology is the efficient filter design process based on the amplitude characteristic analysis with the precise estimation of MC error signal. The experimental result confirmed that almost the same coding performance was maintained at only 30% of the complexity compared to the conventional AIF.

An Enhancement of H.264 Coding Mode for R-D Optimization of Ultra High Resolution Video Coding under Low Bit-rate

So far an efficient coding scheme for ultra high resolution (8K) video under a low bit-rate condition has not yet been proposed. Within H.264 coding framework, highly efficient coding is realized due to the optimal control for the macroblock (MB) coding mode decision. However, coding modes available in H.264 coding are not necessarily appropriate for 8K full resolution coding under the considerably low bit-rate condition, and satisfactory coding performance cannot be achieved within H.264. In this paper, we propose to define the extended coding mode from the analytical result of R-D performance by conventional coding modes. From coding experiments, it was confirmed that the maximum coding gain reached 0.18dB at the target bit-rate assumed in this study.

Adaptive loop filter technology based on analytical design considering local image characteristics

Based on Wiener algorithm, the adaptive loop filter (ALF) technology is applied to minimize coding distortion over a frame. As the ALF is designed based on the Wiener algorithm, coding performance can be improved by spatially adaptive selection of filter coefficients dependent on a local image feature. However, since the conventional ALF approaches designed only a single set of frame basis filter coefficients, the filter coefficients are not necessarily optimal to achieve the significant coding gain. As the conventional work, the modified adaptive loop filter approach that employs the segmentation pattern has been proposed. This approach divides the current frame into a few segments based on the structure of image texture, and the filter coefficients are determined for each segment type. Although 14 candidates are defined as available segmentation modes, further improvement can be expected because such segmentation can not handle the complicated combination of various texture characteristics within a video frame. From this perspective, we propose an enhanced ALF approach based on spatially adaptive control of filter design dependent on the texture property of the local image region. Experimental results show that the bit reduction performance is improved by 1.6 points in the maximum case against the conventional scheme. Furthermore, the proposed scheme contributes to improving the subjective picture quality.

Complementary coding mode design based on R-D cost minimization for extending H.264 coding technology

To improve high resolution video coding efficiency under low bit-rate condition, an appropriate coding mode is required from an R-D optimization (RDO) perspective, although a coding mode defined within the H.264 standard is not always optimal for RDO criteria. With this in mind, we previously proposed extended SKIP modes with close-to-optimal R-D characteristics. However, the additional modes did not always satisfy the optimal R-D characteristics, especially for low bit-rate coding. In this paper, we propose an enhanced coding mode capable of providing a candidate corresponding to the minimum R-D cost by controlling the residual signal associated with the extended SKIP mode. The experimental result showed that the PSNR improvement against H.264 and our previous approach reached 0.42 dB and 0.24 dB in the maximum case, respectively.