Yafan Zhao - Academia.edu (original) (raw)

Papers by Yafan Zhao

IEEE Transactions on Multimedia, Apr 1, 2009

Page 1. IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 11, NO. 3, APRIL 2009 433 Complexity Control of H.2... more Page 1. IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 11, NO. 3, APRIL 2009 433 Complexity Control of H.264/AVC Based on Mode-Conditional Cost Probability Distributions Chaminda Sampath Kannangara, Iain E. Richardson, Maja Bystrom, and Yafan Zhao ...

In this paper we propose a macroblock skip-mode prediction algorithm to reduce the computational ... more In this paper we propose a macroblock skip-mode prediction algorithm to reduce the computational effort of video encoders. The algorithm classifies each macroblock as "skipped" or "not skipped" by estimating the energy of low-frequency quantized coefficients prior to coding, making it possible to significantly reduce computation by not coding these skipped macroblocks Results show that the algorithm can achieve substantial computational savings with only a small degradation in rate-distortion performance.

DCT-based CODECs such as MPEG-4 Visual and H.263 "skip" many macroblocks during encoding of typic... more DCT-based CODECs such as MPEG-4 Visual and H.263 "skip" many macroblocks during encoding of typical video sequences (i.e. no coded data is transmitted for these macroblocks). This paper describes an algorithm that predicts macroblocks that are likely to be skipped by the encoder. The algorithm estimates the increase in distortion due to not coding (skipping) each macroblock. Macroblocks that can be skipped with little or no increase in distortion are not coded, resulting in substantial computational savings without significantly affecting ratedistortion performance.

Variable-complexity algorithms provide a means of managing the computational complexity of a soft... more Variable-complexity algorithms provide a means of managing the computational complexity of a software video CODEC. The reduction in computational complexity provided by existing variable-complexity algorithms depends on the video scene characteristics and is difficult to predict. A new approach to variablecomplexity encoding is proposed in this paper. A variablecomplexity DCT algorithm is adaptively updated in order to maintain a near-constant computational complexity. The adaptive update algorithm is shown to be capable of providing a significant, predictable reduction in computational complexity with only a small loss of video quality. The proposed approach may be particularly useful for software-only video encoding.

Software implementation of block-based video coding standards has been used in a wide range of ap... more Software implementation of block-based video coding standards has been used in a wide range of applications. In many cases, such as real-time multimedia systems or powerconstrained systems, the coding performance of software-only video encoders and decoders is limited by computational complexity. This thesis presents research work to develop techniques to manage computational complexity of video encoders. These techniques aim to provide significant complexity saving as well as adaptively controlling the computational complexity. This thesis first investigates experimentally the most computationally intensive functions in a video encoder. Based on the results of profile tests, several functions are selected as candidates, on which complexity reduction algorithms will be performed. These functions include discrete cosine transform and related functions as well as motion estimation. Adaptive complexity-reduction algorithms are proposed for computationally expensive functions: discrete cosine transform and motion estimation functions respectively. It is shown that these algorithms can flexibly control the computational complexity of each function with negligible loss of video quality. The inherent characteristics of coded macroblocks are investigated through experimental tests and they are categorized into "skipped" and "unskipped7 macroblocks based on two parameters. An innovative algorithm is developed to reduce the computational complexity by predicting "skipped" macroblock prior to encoding and not carrying out the coding process on these macroblocks. The approaches described in this thesis can not only achieve adaptive control of the computational complexity of a video encoder, but also can manage the trade-off between complexity and distortion. These proposed algorithms are evaluated in terms of complexity reduction performance, rate-distortion performance and subjective and objective visual quality by experimental testing. The advantages and disadvantages of each algorithm are discussed. 11 Acknowledgments Writing this part of thesis gives me a formal opportunity to thank the people who have supported me and consequently had influence on the accomplishment of this work within three years. The first acknowledgement goes to Dr lain Richardson who gave me a chance to do this interesting work. I appreciate very much for his constant guidance, suggestions, help and encouragement during this research work. Special thanks are dedicated for the hundreds of discussions we had on almost every working day in the past three years and for reviewing my thesis twice. I also want to thank Dr Tony Miller, Dr Lin Shan and Dr Christos Grecos for being the members of the supervision team and the talks I had with them. They provided useful comments and suggestions. Some people had spent a lot of time on reading my thesis.

IEEE Transactions on Circuits and Systems for Video Technology, Feb 1, 2012

Visual quality of compressed video sequences depends on factors including spatial texture content... more Visual quality of compressed video sequences depends on factors including spatial texture content and cognition-based factors such as prior knowledge and task in hand. The MOSp metric is a full reference objective quality metric which predicts perceived quality of sequences with video compression-induced impairments based on the spatial texture content and the mean squared error between original and compressed video

Signal Processing-image Communication, Oct 1, 2003

Typically, many macroblocks (MBs) are skipped during encoding of H.263 or MPEG-4 SP video data, p... more Typically, many macroblocks (MBs) are skipped during encoding of H.263 or MPEG-4 SP video data, particularly at low bit-rates. In this paper, we describe an algorithm that predicts the occurrence of skipped MBs prior to encoding, making it possible to save significant computational effort by not coding these MBs. The algorithm estimates the energy of low-frequency quantized coefficients in order to classify each MB as 'skipped' or 'not skipped'. Results show that the algorithm can deliver substantial computational savings at the expense of a small reduction in rate-distortion performance.

Real-time imaging, Aug 1, 2002

I n this paper, we investigate methods of reducing the computational complexity of the discrete c... more I n this paper, we investigate methods of reducing the computational complexity of the discrete cosine transform (DCT) in a software video encoder. The number of DCT calculations may be reduced by modeling the distribution of zero blocks. We demonstrate that the reduction in computational complexity is variable and depends on the statistics of the video sequence. We propose a new adaptive algorithm that can maintain a near-constant reduction in complexity. The proposed algorithm performs well at converging to a ''target'' computational complexity, at the expense of a small reduction in image quality. This algorithm provides a flexible mechanism for managing computational complexity in a video encoder.

IEEE Transactions on Circuits and Systems for Video Technology, Feb 1, 2006

IEE International Conference on Visual Information Engineering (VIE 2005), 2005

A complexity reduction algorithm for an H.264 encoder is proposed. Computational savings are achi... more A complexity reduction algorithm for an H.264 encoder is proposed. Computational savings are achieved by identifying, prior to motion estimation, macroblocks that are likely to be skipped and hence saving further computational processing of these macroblocks. This early prediction is made by estimating a Lagrangian rate-distortion cost function which incorporates an adaptive model for the Lagrange multiplier parameter based on local sequence statistics. Simulation results demonstrate that the algorithm can achieve computational savings of 19-65% (depending on the source sequence) with no significant loss of rate-distortion performance.

While the H.264 standard offers improved compression efficiency compared with prior video coding ... more While the H.264 standard offers improved compression efficiency compared with prior video coding standards, this efficiency arises at the cost of significant complexity. We present a reduced complexity coding algorithm which estimates, prior to coding each macroblock, whether the coder would choose the skip or code mode for the macroblock. Computation savings are achieved, since precoding of skipped macroblocks is avoided. The decision to skip a macroblock is based on estimating and modelling mode cost differences, and employing these models in a MAP framework. Results are shown which indicate that for low-activity sequences savings of over 70% in computation time can be achieved with little or no decrease in video quality.

Publication in the conference proceedings of EUSIPCO, Antalya, Turkey, 2005

Multimedia Tools and Applications, 2020

Rate-Distortion (RD) performance of Distributed Video Coding (DVC) is considerably less than that... more Rate-Distortion (RD) performance of Distributed Video Coding (DVC) is considerably less than that of conventional predictive video coding. In order to reduce the performance gap, many methods and techniques have been proposed to improve the coding efficiency of DVC with increased system complexity, especially techniques employed at the encoder such as encoder mode decisions, optimal quantization, hash methods etc., no doubt increase the complexity of the encoder. However, low complexity encoder is a widely desired feature of DVC. In order to improve the coding efficiency while maintaining low complexity encoder, this paper focuses on Distributed Residual Video Coding (DRVC) architecture and proposes a simple encoder scheme. The main contributions of this paper are as follows: 1) propose a bit plane block based method combined with bit plane rearrangement to improve the dependency between source and Side Information (SI), and meanwhile, to reduce the amount of data to be channel encoded 2) present a simple iterative dead-zone quantizer with 3 levels in order to adjust quantization from coarse to fine. The simulation results show that the proposed scheme outperforms DISCOVER scheme for low to medium motion video sequences in terms of RD performance, and maintains a low complexity encoder at the same time. Keywords Distributed residual video coding (DRVC) Bit plane block based Low complexity encoder 1 Introduction Distributed Video Coding (DVC), based on Slepian-Wolf [27] and Wyner-Ziv [34] theorems, is an emerging video coding paradigm and it shifts the computational complexity and storage burdens from encoder to decoder. It encodes video frames independently and decodes them jointly, which is a promising scheme for applications with limited resources [25], such as sensor networks, wireless video surveillance, etc. However, RD performance of DVC is still considerably less than that of conventional motion-compensation based video � Yunhui Xiong

Signal Processing: Image Communication, 2008

In order to achieve a high compression ratio, the H.264/AVC standard has incorporated a large num... more In order to achieve a high compression ratio, the H.264/AVC standard has incorporated a large number of coding modes which must be evaluated during the coding process to determine the optimal rate-distortion tradeoff. The coding gains of H.264/AVC arise at the expense of significant coder complexity which may not be desired for mobile devices with limited battery life. One coder process that has been identified as having potential for achieving computation savings is the selection between skipping the coding of a macroblock and coding of the macroblock in one of the remaining coding modes. In low-motion subsequences, a large percentage of macroblocks are "skipped", that is, no coded data are transmitted for these macroblocks. By estimating which macroblocks are to be skipped during the coding process, significant savings in computation can be realized, since the coder then does not evaluate the ratedistortion costs of all candidate coding modes. In this work we place this skip versus code decision in a Bayesian framework. We use the rate-distortion cost difference between coding and skipping a macroblock as the single decision feature and determine an appropriate decision threshold following modeling of the cost difference's class-conditional PDFs. Finally, in order to further limit system complexity, we model the threshold's parameters as functions of application-and sequence-specific characteristics, namely, the quantization parameter and an activity factor. This results in a decision threshold that is only a function of these two characteristics, which are either known or easily measured. It is shown that this approach can result in a time savings of over 80% for low-motion sequences at a negligible decrease or, in certain cases, a slight increase in quality over a reference H.264 codec.

Typic6v6v many macT4BBvJH (MBs) are skipped duringencngvB of H.263 or MPEG-4 SP video data,partic... more Typic6v6v many macT4BBvJH (MBs) are skipped duringencngvB of H.263 or MPEG-4 SP video data,particBz4vJ at low bit-rates. In this paper, wedesc-BT an algorithm thatpredic` the ocHTqTHvJ of skipped MBs prior toenc4`T`v making it possible to savesignificwv cgnificwvJHH effort by notctvB` these MBs. The algorithm estimates the energy of low-frequenc quantizedcntizedvT- in order tocvBHw4w eac MB as `skipped' or `not skipped'. Results show that the algorithmcg deliver substantial cbstantialvT savings at the expense of a smallreducHz- in rate-distortion performancr r 2003 Else ier B.V. All rights reser ed.

Proceedings of the tenth ACM international conference on Multimedia, 2002

Proceedings 2001 International Conference on Image Processing (Cat. No.01CH37205)

2006 International Conference on Image Processing, 2006