Kiho Choi

Fast coding unit decision method based on coding tree pruning for high efficiency video coding

A fast coding unit (CU) decision method is proposed for high efficiency video coding (HEVC) by determining early the CU sizes based on coding tree pruning. One of the most effective, a newly introduced concept in HEVC, is variable CU size. In determining the best CU size, the reference encoder of the HEVC tests every possible CU size in order to estimate the coding performance of each CU defined by the CU size. This causes major computational complexity within the encoding process, which should be overcome for the implementation of a fast encoder. A simple tree-pruning algorithm is proposed that exploits the observation where the subtree computations can be skipped if the coding mode of the current node is sufficient (e.g., SKIP mode). The experimental results show that the proposed method was able to achieve a 40% reduction in encoding time compared to the HEVC test model 3.0 encoder with only a negligible loss in coding performance. The proposed method was adopted in HEVC test model 4.0 encoder at JCT-VC 6th meeting.

Zero coefficient-aware IDCT algorithm for fast video decoding

Ever since many well-known image and video coding standards such as JPEG, MPEG, and H.26x started using DCT as a core process in data compression, the design of the fast inverse discrete cosine transform (IDCT) has been an intensive research topic. Most research has focused on a reduction of the number of operations using the butterfly structure. However, the majority of DCT coefficients is zero after quantization and is therefore redundant for IDCT computation. Therefore, we exploited this DCT coefficients redundancy to propose a zero coefficient-aware IDCT algorithm for fast decoding. The proposed method significantly reduces the number of IDCT operations by adaptively including non-zero coefficients in the calculation and employing a table look-up to eliminate multiplication operations in the IDCT process. The proposed zero coefficient-ware algorithm outperformed other existing fast IDCT algorithms in terms of operational complexity. Moreover, the running time was faster than butterfly based IDCT algorithms implemented in MPEG-4 simple profile decoder by a speedup factor of 1.32 times for the SIF/CIF sequences and up to 2.18 times for the HD sequences.

Leveraging Parallel Computing in Modern Video Coding Standards

Video coding has always been a computationally intensive process. Although dramatic improvements in coding efficiency have been realized in recent years, the algorithms have become increasingly complex and there is a broader recognition that it is necessary to realize the capabilities of multicore processors. This article discusses how recent trends in parallel computing have influenced the design of modern video coding standards. Specifically, the authors discuss how the High Efficiency Video Coding (HEVC) standard, which is being jointly developed by ISO/IEC JTC1/SC29 WG11 (MPEG) and ITU-T SH16/Q.6 (VCEG), is looking at ways to implement the co-exploration between algorithm and architecture (CEAA) approach.

Zero coefficient-aware fast IQ-IDCT algorithm

In this paper, we propose a zero quantized DCT coefficients-aware algorithm for the implementation of fast inverse quantization (IQ) and inverse discrete cosine transform (IDCT). In our prior work [4], we showed that zero coefficient-ware IDCT algorithm for fast decoding. In this paper, we extended a zero-skipping IDCT (Z-IDCT) by incorporating IQ with Z-IDCT. By adaptively skipping zero quantized coefficient computations, the proposed method can significantly reduce the computation time of IQ and IDCT in decoder. The decoding time of IQ and IDCT using the proposed method showed 36.7 percent speedup on average compared to that of MPEG-4 simple profile, and it also showed 9.6 percent speedup on average compared to that of Z-IDCT with MPEG-4 simple profile.

Unified framework of frame skipping and interpolation for efficient video compression

In this paper, we propose the unified framework of frame skipping and interpolation (UF-FSI) for efficient video compression. Frame skipping and interpolation is one of the efficient approaches to reduce the redundancy of video frames. A joint design of frame skipping and interpolation is made for maximization of compression efficiency, which was not considered from previous research. A good advantage of UF-FSI is that it can be applied to any conventional video codec. Frame skipping in the proposed method is done by selecting key frames through analysis of neighboring frames. In frame interpolation, in-between frames are reconstructed by key frames using motion compensated interpolation. Using with MPEG-4 simple profile, UF-FSI offered additional coding efficiency up to 25 percent with good visual quality.

Data reuse-based fast subpixel motion estimation for high efficiency video coding

Abstract. A data reuse-based fast subpixel motion estimation (SME) method for high efficiency video coding (HEVC) is proposed. Since SME is one of the most computation-intensive tools in the encoder process, conventional research on SME focused on the reduction of the computational complexity. The applied data-reuse architecture for the design of fast SME substantially reduces computational complexity at the cost of a reasonable increase in memory bandwidth. The core of the proposed data-reuse method is the replacement of redundant computations in SME with the memory access operations of previously computed values. The proposed method was tested in the latest video coding standard, HEVC, with experimental results showing a reduction in operational complexity of ∼64.14%, and a reduction in encoding time of ∼56.13%, compared to the SME in the HEVC reference encoder.

Zero coefficient-aware fast butterfly-based inverse discrete cosine transform algorithm

The latest video coding standards, including Moving Picture Experts Group-4 (MPEG-4) advanced video coding (AVC)/H.264 and high-efficiency video coding (HEVC), use a discrete cosine transform (DCT) process as the core for compression efficiency, sacrificing the computational complexity at decoder. There have been a number of attempts to reduce the complexity of inverse DCT (IDCT). Butterfly-based factorisation remains the most commonly used method for such a reduction. In this study, the authors propose a zero (Z) coefficient-aware fast butterfly-based IDCT algorithm for video decoding. They focus on a reduction in the computational complexity of the butterfly-based 8 × 8 IDCT by removing the unnecessary computations of one-dimensional (1D) IDCT kernels, and adaptively applying IDCT kernels based on the number of non-Z DCT coefficients to speed-up 1D data. Their experimental results show that the average operation numbers using the proposed IDCT is approximately half that for the 8 × 8 IDCT implemented in the MPEG-4 AVC/H.264 and HEVC reference software. The improved computational complexity of the proposed method is demonstrated by measuring the running time, which requires only one-half of the IDCT time using the reference software.

An Efficient Parallelization Implementation of PU-level ME for Fast HEVC Encoding

In this paper, we propose an efficient parallelization technique of PU-level motion estimation (ME) in the next generation video coding standard, high efficiency video coding (HEVC) to reduce the time complexity of video encoding. It is difficult to encode video in real-time because ME has significant complexity (i.e., 80 percent at the encoder). In order to solve this problem, various techniques have been studied, and among them is the parallelization, which is carefully concerned in algorithm-level ME design. In this regard, merge estimation method using merge estimation region (MER) that enables ME to be designed in parallel has been proposed; but, parallel ME based on MER has still unconsidered problems to be implemented ideally in HEVC test model (HM). Therefore, we propose two strategies to implement stable parallel ME using MER in HM. Through experimental results, the excellence of our proposed methods is shown; the encoding time using the proposed method is reduced by 25.64 percent on average of that of HM which uses sequential ME.

Fast mode decision for MPEG-4 AVC/H.264 using spatio-temporal correlation

The latest video coding standard, MPEG-4 AVC/H.264 provides the best performance in compression efficiency among existing video coding standards. To achieve higher compression efficiency, AVC/H.264 standard employs a variety of encoding tools but at the expense of greater computational complexity of the encoder. In this paper, we propose a fast mode decision algorithm for the design of a fast AVC/H.264 encoder by exploiting spatio-temporal correlation of macro block (MB) mode types. Through the statistical analysis of encoding mode types in AVC/H.264 JM 11.0, we found that the best mode type of the current MB is highly correlated with the mode types of spatially neighboring MBs and temporally collocated MBs. The experimental results showed that AVC/H.264 encoder using our proposed method produced about 66 % speedup without noticeable visual degradation compared to the AVC/H.264 JM 11.0 encoder.

CU depth-based ALF decision for fast HEVC encoding

In this paper, we propose a coding unit (CU) depth-based adaptive loop filter (ALF) decision method to reduce the encoder complexity. In high efficiency video coding (HEVC), ALF is designed based on Wiener filter to minimize the distortion between the original frame and the coded frame. In order to design the optimal filter for each CU, the filter design process is repeated 12 times per CU. The repetition of the filter design process occupies about 77 percent in the total ALF computation time, which substantially increases the encoder complexity. The proposed method simplifies the filter design with the CU depth-based ALF decision, which is based on the observation by exploiting ineffective computations. Experimental results show that the proposed method reduces the encoding time for the repetition of the filter design process by about 13 percent of that of the HEVC test model (i.e., HM 5.0) with 0.1 percent BD-rate increase.