KEYWORDS: Video coding, High efficiency video coding, Chromium, Design and modelling, Artificial intelligence, Video compression, Tunable filters, Statistical analysis, Smoothing, Interpolation
Versatile Video Coding (VVC) procured an impressive coding gain with the help of various new coding tools. In the case of intra chroma coding, chroma separate tree (CST) and cross-component linear model (CCLM) show remarkable coding gain. However, there are only 8 prediction mode candidates in intra chroma coding which is much fewer than the 67 prediction mode candidates and up to 32 matrix-weighted intra prediction (MIP) mode candidates in intra luma coding. Excluding the three CCLM modes, the number of intra prediction mode candidates for chroma is just five, which is less than one tenth of luma channel which uses 67 intra prediction mode candidates except the MIP modes. In this paper, we investigate adding one more intra chroma prediction mode whose prediction direction is derived from the neighboring reconstructed area. The proposed method achieves a BDBR gain of 0.36% and 0.26% in the Cb and Cr channels without loss in Y channel under the all intra configuration.
Multiple reference line (MRL) intra prediction allows to use reference lines not necessarily immediately adjacent neighboring line or column in generating intra predictor. Compared to MRL already existing in the versatile video coding (VVC) standard which can use a total of three reference lines including the adjacent one, the MRL under discussion now in enhanced compression beyond VVC is extended to use a total of six reference lines. However, its MRL candidates are listed in a fixed order for all blocks without considering non-identical effectiveness of each reference line in intra prediction. In this paper, we propose a reordering scheme of the MRL candidate lines in the MRL list considering similarities between predictors generated by available reference lines. According to our experimental results, the proposed method is shown to achieve an overall coding gain of -0.02% in luma channel over the enhanced compression model (ECM) 5.0 under the all intra (AI) configuration of the common test condition (CTC).
KEYWORDS: Video coding, Displays, Quantization, Video, Statistical analysis, Video compression, Cameras, Artificial intelligence, Virtual reality, High efficiency video coding
Rate-distortion optimized quantization for transform skip (RDOQ-TS) is shown to provide positive coding gain in VVC. This paper reduces encoding time-complexity of the RDOQ-TS scheme in VVC by adaptively skipping its level estimation (LE) process without sacrificing coding efficiency much. At first, the characteristics of each quantized level by RDOQ-TS are analyzed statistically. Subsequently, based on the statistical analysis, the LE process in the RDOQ-TS process is simplified by removing the case where the SQ (Scalar Quantization) value and the finally determined value are highly expected to be the same. For 4:2:0 screen content videos and 4:4:4 screen content videos, our proposed simplified rate-distortion optimization for transform skip reduces total encoding time respectively by 0.77% and 1.83% with no BDBR change under all intra configuration. In the case of the random access configuration, it achieves bit rate saving by -0.01 % and -0.03 % with total encoding time reduced 0.94% and 0.52% respectively.
The CST (Chroma Separate Tree) coding tool in VVC (Versatile Video Coding) allows different partition structures in the luma and chroma channels, and it gives significant coding efficiency for the chroma channel. Under CST, the DM mode can be less efficient when the current chroma block and its co-located luma block have different block shapes and sizes, thus less correlated. To solve this potential problem, we investigate a slightly modified DM mode, so called MPDM (Most Probable Direct Mode), to increase coding efficiency of the chroma intra coding. The proposed method is shown to achieve BDBR gain of -0.03% in the Y channel, -0.25% and -0.24% in the Cb and Cr channels, respectively.
Since MPEG and VCEG jointly standardized the H.265/HEVC (High-Efficiency Video Coding) international standard in 2013, they have just completed H.266/VVC (Versatile Video Coding) [1] as the Final Draft International Standard (FDIS) in July 2020 through the Joint Video Experts Team (JVET) of ISO / IEC JTC1 / SC29 / WG11 MPEG and ITU-T SG16 / Q6 VCEG. VVC supports up to 87 intra coding modes including 65 general directional modes and 20 wide angular modes, which is increased more than twice compared to HEVC. VVC can accommodate not only more detailed intra prediction directions, but also so called wide angular modes which make its special sense in non-square coding blocks. The more detailed intra predictions naturally demand more computation in order to determine the most effective intra-prediction mode. In this sense, we investigate how to pre-prune the prediction candidate lists for a fast ISP intra mode decision and propose searching only a small number of prediction modes based on the shape of a block in the rate-distortion optimization (RDO)–based intra mode decision. The proposed method is verified to decrease the intra prediction processing time with only a little increase in the bit rate and a negligible reduction in PSNR values.
KEYWORDS: Video coding, Video compression, Video, Computer programming, Chromium, High dynamic range imaging, Standards development, Binary data, Computer engineering, Information theory
The Versatile Video Coding (VVC) is a new state-of-the art video compression technology that is being under standardization. It targets for about two times higher coding efficiency against the existing HEVC, supporting HD/UHD/8K video and high dynamic range (HDR) video. It also targets for versatilities such as screen content coding, adaptive resolution change, and independent sub-pictures. To develop an effective coding method for chroma intra prediction mode, in this paper, we investigate its binarization process in CABAC (context adaptive binary arithmetic coding) and test a method which assigns shorter bins to more frequent chroma intra modes and longer bins to the less frequent ones based on the chroma mode statistics.
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