International Core Journal of Engineering 2020-26 | Page 170

2019 International Conference on Artificial Intelligence and Advanced Manufacturing (AIAM) Improve the Efficiency of Low Frequency Non- Separable Secondary Transform Based on Implicit Multiple Transform Selection Zhu Hong Jucai Lin R & D Center Zhejiang Dahua Technology Co.,Ltd Hangzhou, China [email protected] R & D Center Zhejiang Dahua Technology Co.,Ltd Hangzhou, China [email protected] Dong Jiang Jun Yin R & D Center Zhejiang Dahua Technology Co.,Ltd Hangzhou, China [email protected] R & D Center Zhejiang Dahua Technology Co.,Ltd Hangzhou, China [email protected] Abstract—In order to effectively adapt to the dynamic transformation characteristics of the residual, multiple transform selection (MTS) was accepted in next generation video coding standard. The MTS can be divided into explicit MTS and implicit MTS, the difference between them was that the primary transform pairs are different, and the primary transform pair of implicit MTS can be determined uniquely by the size of the input block. However, the MTS is a separable transform, the compression capability is limited. So the Low Frequency Non-Separable Secondary Transform (LFNST) was adopted to perform the second transform in primary transform coefficients. But LFNST does not separate the difference between explicit MTS and implicit MTS, which would have effect on performance of LFNST. In this paper, when implicit MTS is enabled, we proposed that if primary transform pair is a combination of DCT2 (Discrete Cosine Transform type II) and DST7 (Discrete Sine Transform type VII), replacing DST7 by DCT2. Two schemes were designed and tested. The experimental results show that the proposed two schemes achieved 0.09% and 0.16% luma BD-rate reduction for all intra configurations respectively, and coding running time complexity nearly constant. transform is adopted in H264 [1]. On the basis of H264, HEVC (High Efficiency Video Coding) enlarges the size of integer DCT2 transform, and also introduces DST7 (Discrete Sine Transform type VII) transform into intra prediction 4*4 luma residual blocks [2]. The transforms were based on fixed image statistical assumptions, both in the H264 and HEVC. However, the prediction residuals have dynamic transformation characters in actual image, and the simplicity of the transform kernel limits the coding gain. In order to better adapt to the dynamic transformation characteristics of the residual, Zhao et al. proposed enhanced multiple transform (EMT) for video coding, the experimental results show that the EMT significantly improves the coding efficiency [4]. The scheme defines three transform sets, each transform set contains two transform bases in DST7, DST1 (Discrete Sine Transform type II), DCT5 (Discrete Cosine Transform type V) and DCT8, and the selection of the transform set is related to the intra prediction mode. In 2018 Ljubljana meeting, EMT was simplified and renamed MTS (Multiple transform selection), which is applicable only to luma components [5]. Only two transform bases, DST7 and DCT8 (Discrete Cosine Transform type VIII) were retained, and the dependence of selection of transform set on intra prediction mode was eliminated. The combination of MTS and DCT2 constitutes the main content of the primary transform has been adopted in the VTM5.0 [6] reference software for developing the next-generation video coding technologies. Keywords—next generation video coding; implicit multiple transform selection; low frequency non-separable secondary transform I. I NTRODUCTION Transform is a very important part of the video coding standard. The transform process can remove the spatial correlation of data, and further achieve the purpose of compressing data through quantization and entropy coding [1-2]. In theory, KLT (Karhunen-Loeve Transform) [3] is the optimal transform to remove the correlation between the signals. However, KLT is difficult to implement because without fast algorithms. Therefore, it is necessary to find a transform that the performance is similar to KLT and easy to implement. The DCT2 (Discrete Cosine Transform type II) is an acceptable transform for KLT, exerting similar performance with easier implement. The 4*4 integer DCT2 978-1-7281-4691-1/19/$31.00 ©2019 IEEE DOI 10.1109/AIAM48774.2019.00037 The MTS contains implicit MTS and explicit MTS, which cannot exist at the same time, explicit MTS is enabled by default. The type of horizontal and vertical transform defaults to DCT2, when explicit MTS is enabled, the explicit MTS transform selection can have the following pairs: (DCT8, DCT8), (DCT8, DST7), (DST7, DCT8), (DST7, DST7). There is need to traverse all of transform pairs to select the best transform. When implicit MTS is enabled, it is judged whether to change the transform type to DST7 according to the size of the input block. Therefore, there are 148