Tomoo Yamakage

A single-chip MPEG-2 codec based on customizable media embedded processor

A single-chip MPEG-2 MP@ML codec, integrating 3.8M gates on a 72-mm/sup 2/ die, is described. The codec employs a heterogeneous multiprocessor architecture in which six microprocessors with the same instruction set but different customization execute specific tasks such as video and audio concurrently. The microprocessor, developed for digital media processing, provides various extensions such as a very-long-instruction-word coprocessor, digital signal processor instructions, and hardware engines. Making full use of the extensions and optimizing the architecture of each microprocessor based upon the nature of specific tasks, the chip can execute not only MPEG-2 MP@ML video/audio/system encoding and decoding concurrently, but also MPEG-2 MP@HL decoding in real time.

Adaptive Loop Filtering for Video Coding

Adaptive loop filtering for video coding is to minimize the mean square error between original samples and decoded samples by using Wiener-based adaptive filter. The proposed ALF is located at the last processing stage for each picture and can be regarded as a tool to catch and fix artifacts from previous stages. The suitable filter coefficients are determined by the encoder and explicitly signaled to the decoder. In order to achieve better coding efficiency, especially for high resolution videos, local adaptation is used for luma signals by applying different filters to different regions or blocks in a picture. In addition to filter adaptation, filter on/off control at coding tree unit (CTU) level is also helpful for improving coding efficiency. Syntax-wise, filter coefficients are sent in a picture level header called adaptation parameter set, and filter on/off flags of CTUs are interleaved at CTU level in the slice data. This syntax design not only supports picture level optimization but also achieves a low encoding latency. Simulation results show that the ALF can achieve on average 7% bit rate reduction for 25 HD sequences. The run time increases are 1% and 10% for encoders and decoders, respectively, without special attention to optimization in C++ code.

In-loop filter using block-based filter control for video coding

In this paper, a method of improving coding efficiency is proposed by using the Wiener filter as an in-loop filter. The Wiener filter can minimize the mean square error between the input image and the decoded image. However, errors of some pixels increase by filtering process. Since the filtered pixels are used for motion-compensated prediction, these errors are propagated to the subsequent images. The proposed method divides the decoded image into some fixed blocks, and decides whether to apply the filter for each block adaptively. As a result, by preventing the increase in errors after the filtering process, the coding efficiency can be improved. Experimental results show that the proposed method achieves bitrate reduction of up to 33.9% in Baseline Profile and up to 33.0 % in High Profile at the same PSNR compared to H.264.

A single-chip MPEG-2 codec based on customizable media microprocessor

A single-chip MPEG2 MP@ML codec, integrating 3.8M gates on a 72mm/sup 2/ die, is described. It has a heterogeneous multiprocessor architecture in which six microprocessors with the same instruction set but different customization execute specific tasks such as video, audio etc. concurrently. The microprocessor, developed for digital media processing, provides various extensions such as a VLIW one and a DSP one inherent in its architecture. Making full use of the extensions, the chip executes encoding and decoding of video, audio and system concurrently in real time.

The adaptive loop filtering techniques in the HEVC standard

This article introduces adaptive loop filtering (ALF) techniques being considered for the HEVC standard. The key idea of ALF is to minimize the mean square error between original pixels and decoded pixels using Wiener-based adaptive filter coefficients. ALF is located at the last processing stage of each picture and can be regarded as a tool trying to catch and fix artifacts from previous stages. The suitable filter coefficients are determined by the encoder and explicitly signaled to the decoder. In order to achieve better coding efficiency, especially for high resolution videos, local adaptation is used for luma signals by applying different filter to different region in a picture. In addition to filter adaptation, filter on/off control at largest coding unit (LCU) level is also helpful for improving coding efficiency. Syntax-wise, filter coefficients are sent in a picture level header called adaptation parameter set (APS), and filter on/off flags of LCUs are interleaved at LCU level in the slice data. Besides supporting picture-based optimization of ALF, the syntax design can support low delay applications as well. When the filter coefficients in APS are trained by using a previous picture, filter on/off decisions can be made on the fly during encoding of LCUs, so the encoding latency is only one LCU. Simulation results show that the ALF can achieve on average 5% bit rate reduction and up to 27% bit rate reduction for 25 HD sequences. The run time increases are 1% and 10% for encoders and decoders, respectively, with un-optimized C++ codes in software.

Multi-directional implicit weighted prediction based on image characteristics of reference pictures for inter coding

Weighted prediction (WP) in H.264/MPEG-4 AVC (H.264) is an efficient motion compensation technique to predict illumination variation and consists of two modes: an explicit WP (EWP) and an implicit WP (IWP). Since in IWP, only weighting factors are implicitly derived from reference pictures used for bi-prediction, and the offsets are always set to 0, there are issues in that IWP cannot utilize the optimal WP parameters, and cannot be applied to uni-prediction. In order to overcome these issues, this paper presents a novel decoding process to derive WP parameters implicitly by using the Multi-Directional Implicit Weighted Prediction (MD-IWP) method. WP parameters are derived using the image characteristics of reference pictures. By linearly predicting the image characteristics of the target picture using different reference pictures stored in the decoded picture buffer, WP parameters of uni-prediction can also be derived. This method can achieve 15% to 50% bitrate reduction compared to the conventional IWP method. This gain is almost the same or better than in the case of EWP with the simple 1-pass parameter estimation method.

One-Dimensional Directional Unified Transform for intra coding

In this paper, we present the One-Dimensional Directional Unified Transform (1DDUT) for intra coding. Intra prediction in H.264/AVC has eight different directional prediction modes and a DC prediction mode. Since the statistical characteristics of prediction residuals are different in each prediction mode, coding efficiency can be improved by applying the different optimal transform for each prediction mode. However, in order to avoid the increase of the complexity, unification of the transforms is desired. Therefore we classify the characteristics of the prediction residuals along the vertical or the horizontal direction, where each direction has two classes and their characteristics are similar to each other between directions. It is sufficient to use two kinds of 1-D transforms that are designed based on the unified characteristics. One is the well-known Discrete Cosine Transform, and the other is a predetermined 1-D transform based on the Karhunen-Loeve Transform method. 1DDUT switches DCT and the predetermined 1-D transform according to the intra prediction modes. 1DDUT can achieve 8.71% bitrate reduction on average with negligible complexity increase compared to the DCT-like transform used in H.264/AVC.