Hisao Sasai

Frame-rate up-conversion using reliable analysis of transmitted motion information

We propose a new frame-rate up-conversion algorithm using a vector reliable analysis scheme that reduces artifacts caused by the use of inaccurately transmitted motion vectors (MVs). In conventional up-conversion algorithms using motion estimation (ME), ME is performed between two adjacent decoded frames to construct MVs that allow the frame to be interpolated, irrespective of the amount of calculation for ME required. On the other hand, in conventional up-conversion algorithms using transmitted MVs, the quality of the interpolated frame depends largely on the MV that is derived by the encoder. In our proposed scheme, transmitted MVs are first analyzed to decide whether or not they are usable for constructing interpolation frames. The interpolation method is then adaptively selected from three methods: local motion-compensated interpolation, global motion-compensated interpolation and frame-repeated interpolation. The proposed method provides high quality interpolated frames and decreases the volume of calculation needed, making it especially well suited to multimedia mobile devices that depend on low-power processing.

Video Coding Using a Simplified Block Structure and Advanced Coding Techniques

This paper describes a new video coding scheme based on a simplified block structure that significantly outperforms the coding efficiency of the ISO/IEC 14496-10 ITU-T H.264 advanced video coding (AVC) standard. Its conceptual design is similar to a typical block-based hybrid coder applying prediction and subsequent prediction error coding. The basic coding unit is an 8 × 8 block for inter, and an 8 × 8 or a 16 × 16 block for intra, instead of the usual 16 × 16 macroblock. No larger block sizes are considered for prediction and transform. Based on this simplified block structure, the coding scheme uses simple and fundamental coding tools with optimized encoding algorithms. In particular, the motion representation is based on a minimum partitioning with blocks sharing motion borders. In addition, compared to AVC, the new and improved coding techniques include: block-based intensity compensation, motion vector competition, adaptive motion vector resolution, adaptive interpolation filters, edge-based intra prediction and enhanced chrominance prediction, intra template matching, larger trans forms and adaptive switchable transforms selection for intra and inter blocks, and nonlinear and frame-adaptive de-noising loop filters. Finally, the entropy coder uses a generic flexible zero tree representation applied to both motion and texture data. Attention has also been given to algorithm designs that facilitate parallelization. Compared to AVC, the new coding scheme offers clear benefits in terms of subjective video quality at the same bit rate. Objective quality improvements are equally significant. At the same quality, an average bit-rate reduction of 31% compared to AVC is reported.

Tree structured hybrid intra prediction

This paper proposes a new method to generate intra prediction images in intra coding, tree structured hybrid intra prediction. When generating intra prediction images, the proposed method selects the most suitable one from intra prediction images generated using two methods, pixel-based and block-based intra prediction. This selection is performed on macroblock or sub macroblock level based on a rate distortion optimization scheme. In addition, information indicating which prediction method is selected is described in the bitstream using a tree structure. The proposed method is initially described, and then the results of evaluation experiments are shown by comparison to conventional methods. Evaluation is carried out by implementing the proposed method in an H.264-based intra picture codec. The results of evaluation confirm that the proposed method improves PSNR by up to nearly 0.7 dB compared to conventional methods over a wide range of bit rates.

B-picture coding with motion-compensated frame rate upconversion

In this paper, we propose a new method to improve the coding efficiency of B-pictures by applying a motion compensated frame rate up-conversion technique. In B-Picture coding in H.264, direct mode is used for one of the prediction modes. In the direct mode, B-picture is constructed without transmitted motion vector information. Consequently, the direct mode is the most effective coding mode in B-picture coding. On the other hand, in motion compensated frame rate up-conversion technique, interpolated frames which are similar to B-pictures, can be constructed with the motion vectors by detecting motion between coded images. In our proposed method, the same motion estimation algorithm is used for detecting motion vectors between reference P-pictures in both of encoder side and decoder side. Our proposed decoder can use the detected motion vectors without transmitted motion vector information for B-picture coding. In the experiment, we selected prediction modes for each block by using conventional rate distortion optimization algorithm. The proposed method improves B-picture coding efficiency by nearly 30% over than that of H.264.