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학술지 Subsampled Sum-Modified-Laplacian for Adaptive Loop Filter in Versatile Video Coding
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임성창, 김명준, 강정원, 이영렬
IEEE Access, v.8, pp.176330-176342
20HH2500, [전문연구실] 6DoF 입체공간 비디오의 초고압축 부호화 기술 개발 및 표준화, 강정원
This paper proposes a Subsampled Sum-Modified-Laplacian (SSML) operator for the block classification of the Adaptive Loop Filter (ALF) in Versatile Video Coding (VVC). The VVC Test Model (VTM)-2.0 includes Geometry transformation-based ALF (GALF) with 4 4 block classification, a single 7 7 Luma diamond-shaped filter, and spatial adaptation at the Coding Tree Block (CTB) level to improve the coding efficiency of VVC. However, in the 4 4 block classification, 1-D (1-Dimensional) Modified-Laplacian (ML) values for various directions are calculated at all sample positions within an 8 8 window, and these are summed to derive the gradients for the corresponding directions. For a CTB where theWiener filter is applied, every 4 4 Luma block within the CTB must calculate Sum-Modified-Laplacian (SML) operations, which results in increased computational complexity of the decoder. Therefore, four different subsampling patterns based on 4 4 block classification for the SSML operator that calculate the 1-D ML values at subsampled sample positions within the 8 8 window are proposed as attempts to reduce the computational complexity of the block classification process in the ALF of VTM-2.0. As all of the proposed subsampling patterns reduce the number of sample positions needed to calculate the 1-D ML operations by half, the experimental results demonstrate that the proposed method achieves total decoding time reductions in the range of 2% to 3%, while the coding gain of the ALF is maintained.
KSP 제안 키워드
Block classification, Classification process, Coding Gain, Coding Tree Block(CTB), Coding efficiency, Computational complexity, Decoding time, Diamond-shaped, Sum-modified-laplacian(SML), Video coding, adaptive loop filter
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