• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.379-385
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• 2015

This paper proposes the hardware architecture of high performance ALF(Adaptive Loop Filter) for efficient filter coefficient estimation. In order to make the original image which has high resolution and high quality into highly compressed image effectively and also, subjective image quality into improved image, the ALF technique of HEVC performs a filtering by estimating filter coefficients using statistical characteristics of image. The proposed ALF hardware architecture is designed with a 2-step pipelined architecture for a reduction in performance cycle by analysing an operation relationship of Cholesky decomposition for the filter coefficient estimation. Also, in the operation process of the Cholesky decomposition, a square root operation is designed to reduce logic area, computation time and computation complexity by using the multiplexer, subtracter and comparator. The proposed hardware architecture is designed using Xilinx ISE 14.3 Vertex-7 XC7VCX485T FPGA device and can support 4K UHD@40fps in real time at a maximum operation frequency of 186MHz.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.2
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• pp.93-101
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• 2017

This paper proposes an algorithm for adaptive loop filter (ALF) complexity reduction in the decoding process. In the original ALF algorithm, filtering for I frames is performed in the frame unit, and thus, all of the pixels in a frame are filtered if the current frame is an I frame. The proposed algorithm is designed on top of the local gradient calculation. On both the encoder side and the decoder side, homogeneous areas are checked and skipped in the filtering process, and the filter coefficient calculation is only performed in the inhomogeneous areas. The proposed algorithm is implemented in Joint Exploration Model (JEM) version 3.0 future video coding reference software. The proposed algorithm is applied for frame-level filtering and intra configuration. Compared with the JEM 3.0 anchor, the proposed algorithm has 0.31%, 0.76% and 0.73% bit rate loss for luma (Y) and chroma (U and V), respectively, with about an 8% decrease in decoding time.

• Journal of Broadcast Engineering
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• v.18 no.2
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• pp.261-270
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• 2013

A stereoscopic 3D video service is able to provide a 3D video service while keeping backward compatibility with the existing 2D video service. In the terrestrial digital television (DTV) system, a stereoscopic video codec is required to have high coding efficiency in order to provide a 3D video service in the same channel capacity. A hybrid codec consisting of MPEG-2 for base video and H.264/AVC or HEVC for 3D auxiliary video is considered. Furthermore, Non-Real-Time (NRT) delivery of stereoscopic video is also considered as a service scenario for 3DTV services to overcome the limited bandwidth. In this paper, we propose a stereoscopic video coding scheme using adaptive loop filter (ALF) which had been considered in HEVC as a pre-/post-filter for enhancing coding efficiency in NRT-based 3DTV services. In order to apply ALF as a post-filter to the reconstructed additional view coded by H.264/AVC, we devise a method in which ALF is adaptively applied based on a structure determined by using macroblock (MB) coding information such as MB mode type and reference index instead of coding unit (CU) structure on which ALF is applied in the HEVC. Experimental results shows that the proposed stereoscopic video coding scheme applying ALF obtains up to 24.9% gain of bit saving.

• Journal of Broadcast Engineering
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• v.15 no.5
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• pp.617-630
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• 2010

At 37th VCEG meeting in Jan. 2009, Toshiba proposed Quadtree-based Adaptive Loop Filter (QALF). The basic concept of QALF is to apply Wiener filter to decoded image after the conventional deblocking filter and to represent the filter on/off flag data for each basic filtering unit in a more efficient way of quadtree structure. QALF could enhance the compression performance of around more than 9%, but the structure of one filter for a decoded frame leaves room for further improvement in the sense that optimal filter for one region of a frame could quite different from the optimal filter for other parts of a picture. This paper proposes multiple adaptive loop filters for better utilization of local characteristics of decoded frame to optimize the region-based Wiener filters. Additional filters, proposed in this paper, cover separate spatial area of each decoded frame according to the performance of previously designed filter(s) to provide the flexibility of rate-distortion based selection of the number of filters.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.295-298
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• 2014

In this paper, an efficient design of HEVC Adaptive Loop Filter(ALF) for filter coefficients estimation is proposed. The ALF performs Cholesky decomposition of $10{\times}10$ matrix iteratively to estimate filter coefficients. The Cholesky decomposition of the ALF consists of root and division operation which is difficult to implement in a hardware design because it needs to many computation rate and processing time due to floating-point unit operation of large values of the Maximum 30bit in a LCU($64{\times}64$). The proposed hardware architecture is implemented by designing a root operation based on Cholesky decomposition by using multiplexer, subtracter and comparator. In addition, The proposed hardware architecture of efficient and low computation rate is implemented by designing a pipeline architecture using characteristic operation steps of Cholesky decomposition. An implemented hardware is designed using Xilinx ISE 14.3 Vertex-6 XC6VCX240T FPGA device and can support a frame rate of 40 4K Ultra HD($4096{\times}2160$) frames per second at maximum operation frequency 150MHz.

• Broadcasting and Media Magazine
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• v.24 no.4
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• pp.87-101
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• 2019

JVET(Joint Video Experts Team)에서 새로운 비디오 압축 표준으로 진행 중인 VVC(Versatile Video Coding)에서는 HEVC(High Efficiency Video Coding)의 기술을 근간으로 부호화 효율을 높일 수 있는 다양한 새로운 기술들을 채택하고 있다. 인루프 필터(In-Loop Filter)는 복원영상의 화질을 향상시키기 위한 기술로 주관적 화질 개선뿐만 아니라 부호화 효율을 향상시키는 기술로 기존 HEVC의 확장 기술 및 새로운 인루프 필터 기술을 채택하고 있다. 본 고에서는 VVC의 CD에 채택되어 있는 인루프 필터 기술들을 소개한다. 인루프 필터 기술은 HEVC에 채택되어 있는 디블록킹 필터(Deblocking Filter: DF)와 SAO(Sample Adaptive Offset), 새로이 추가된 ALF(Adaptive Loop Filter)의 3가지의 필터와 LMCS(Luma Mapping with Chroma Scaling) 기술을 포함하고 있다. 이들 인루프 필터 기술은 주관적 화질 개선과 부호화 효율을 크게 개선하고 있으며, 2020년 7월 FDIS(Final Draft International Standard) 완료를 앞두고 인루프 필터링의 다양화로 인한 성능과 복잡도를 고려한 간소화 및 병렬처리 등의 고속화에 대한 표준화가 지속적으로 이루어질 전망이다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2020.11a
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• pp.143-144
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• 2020

VVC (Versatile Video Coding)는 HEVC이후 차세대 표준 비디오 코딩으로 JVET(Joint Video Exploration)에 의해 2018년 표준화를 시작하였다. VVC에는 복원픽쳐의 변환-양자화에러에 의해 발생한 블로어, 블로킹, 링잉 아티팩트를 감소시키기 위하여 deblocking filter (DF), sample adaptive offset (SAO), adaptive loop filter(ALF)와 같은 모듈을 사용한다. 한편 CNN (Convolutional Neural Network)은 최근 이미지와 비디오 복원에 높은 성능을 보이고 있다. VVC에서 픽쳐는 CTU (Coding Tree Unit)으로 분할되고 각 CTU는 다시 CU (Coding Unit)으로 분할된다. 그리고 인코딩을 위한 중요한 정보들이 Picture, CTU, CU단위로 디코더에 전송된다. 이 논문에서는 화면 간 예측으로 인코딩 된 픽처에서 블록과 픽처정보를 이용한 딥러닝 기반의 인루프 필터 모델을 제안한다. 제안하는 모델은 화면 간 예측에서 QP, 4×4 블록단위의 모션벡터, 참조블록과의 시간적거리, CU의 깊이를 모델에 추가적인 정보로 이용한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.378-380
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• 2011

스테레오스코픽(stereoscopic) 3D 비디오 서비스는 기존 2D 와의 호환성을 유지하면서 새로운 3D 비디오 서비스를 제공할 수 있는 것으로, 전송 대역이 제한된 지상파 방송에서 높은 부호화 효율을 갖는 스테레오스코픽 비디오 코덱이 요구된다. 따라서 3D 를 위한 부가영상의 부호화를 위해 H.264/AVC 등을 고려하고 있으며, 또한 부가영상을 비실시간으로 전송하는 비실시간(Non-Real Time: NRT) 3D 서비스도 고려되고 있다. 본 논문에서는 NRT 3D 서비스를 위한 스테레오스코픽 비디오 부호화에 있어서, HEVC 에서 고려중인 적응루프필터(ALF: Adaptive Loop Filter)를 전/후처리 필터로 적용하는 기법을 제시한다. 특히, 부가영상의 후처리에 ALF 를 적용하기 위하여 부호화 과정에 결정되는 CU(Coding Unit) 구조를 이용하는 HEVC 와 달리 H.264/MVC 로 부호화한 부가영상의 매크로블록(MB) 부호화 모드를 이용한 ALF 적용 기법을 제안한다. 부가영상 부호화에 있어서 전처리 및 후처리 과정으로 ALF 를 적용함으로써 최대 약 20.5%의 부가영상의 부호화 성능 향상을 확인하였다.

• ETRI Journal
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• v.34 no.5
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• pp.666-673
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• 2012

Non-real-time delivery of stereoscopic video has been considered as a service scenario for 3DTV to overcome the limited bandwidth in the terrestrial digital television system. A hybrid codec combining MPEG-2 and H.264/AVC has been suggested for the compression of stereoscopic video for 3DTV. In this paper, we propose a stereoscopic video coding scheme using adaptive pre-/post-filters (APPF) to improve the quality of 3D video while retaining compatibility with legacy video coding standards. The APPF are applied adaptively to blocks of various sizes determined by the macroblock coding mode and reference frame index. Experiment results show that the proposed method achieves up to 24.86% bit rate savings relative to a hybrid codec of MPEG-2 and H.264/AVC including the inter-view prediction.