This paper presents the intra prediction and mode coding of the Versatile Video Coding (VVC) standard. This standard was collaboratively developed by the Joint Video Experts Team (JVET). It follows the traditional architecture of a hybrid block-based codec that was also the basis of previous standards. Almost all intra prediction features of VVC either contain substantial modifications in comparison with its predecessor H.265/HEVC or were newly added. The key aspects of these tools are the following: 65 angular intra prediction modes with block shape-adaptive directions and 4-tap interpolation filters are supported as well as the DC and Planar mode, Position Dependent Prediction Combination is applied for most of these modes, Multiple Reference Line Prediction can be used, an intra block can be further subdivided by the Intra Subpartition mode, Matrix-based Intra Prediction is supported, and the chroma prediction signal can be generated by the Cross Component Linear Model method. Finally, the intra prediction mode in VVC is coded separately for luma and chroma. Here, a Most Probable Mode list containing six modes is applied for luma. The individual compression performance of tools is reported in this paper. For the full VVC intra codec, a bitrate saving of 25% on average is reported over H.265/HEVC using an objective metric. Significant subjective benefits are illustrated with specific examples.

Lossy compression is the main target of the upcoming video coding standard Versatile Video Coding (VVC). However, lossless coding is supported in VVC by utilizing a certain encoder configuration. Particularly, the Transform Skip Mode (TSM) is always selected at the block level to bypass the transform stage (together with a QP that results in the same output as input at the quantization stage). Consequently, the Intra Subpartition (ISP) coding mode cannot be used for lossless coding, considering that its combination with TSM is not supported in VVC because it does not provide a significant coding benefit for the lossy common test conditions. For this reason, it is proposed to enable such a combination for the benefit of lossless coding. Besides, the encoder search has been optimized to improve the trade-off between compression benefit and encoder run-time. Experimental results show a 0.71% coding gain with a corresponding encoder run-time of 111%.

The Intra Subpartition (ISP) mode is one of the intra prediction tools incorporated to the new Versatile Video Coding (VVC) standard. ISP divides a luma intra-predicted block along one dimension into 2 or 4 smaller blocks, called subpartitions, that are predicted using the same intra mode. This paper describes the design of this tool and its encoder search implementation in the VVC Test Model 7.3 (VTM-7.3) software. The main challenge of the ISP encoder search is the fact that the mode pre-selection based on the sum of absolute transformed differences typically utilized for intra prediction tools is not feasible in the ISP case, given that it would require knowing beforehand the values of the reconstructed samples of the subpartitions. For this reason, VTM employs a different strategy aimed to overcome this issue. The experimental tool-off tests carried out for the All Intra configuration show a gain of 0.52% for the 22-37 Quantization Parameter (QP) range with an associated encoder runtime of 85%. The results are improved to a 1.06% gain and an 87% encoder runtime in the case of the 32-47 QP range. Analogously, for the tool-on case the results for the 22-37 QP range are a 1.17% gain and a 134% encoder runtime and this improves in the 32-47 QP range to a 1.56% gain and a 126% encoder runtime.

In this paper, we describe a video coding design that enables a higher coding efficiency than the HEVC standard. The proposed video codec follows the design of block-based hybrid video coding, but includes a number of advanced coding tools. A part of the incorporated advanced concepts was developed by the Joint Video Exploration Team, while others are newly proposed. The key aspects of these newly proposed tools are the following. A video frame is subdivided into rectangles of variable size using a binary partitioning with variable split ratios. Three new approaches for generating spatial intra prediction signals are supported: A line-wise application of conventional intra prediction modes, coupled with a mode-dependent processing order, a region-based template matching prediction method and intra prediction modes based on neural networks. For motion-compensated prediction, a multi-hypothesis mode with more than two motion hypotheses can be used. In transform coding, mode dependent combinations of primary and secondary transforms are applied. Moreover, scalar quantization is replaced by trellis-coded quantization and the entropy coding of the quantized transform coefficients is improved. The intra and inter prediction signals can be filtered using an edge-preserving diffusion filter or a non-linear DCT-based thresholding operation. The video codec includes an adaptive in-loop filter for which one of three classifiers can be chosen on a picture basis. We also incorporated an optional encoder control, which adjusts the quantization parameters based on a perceptually motivated distortion measure. In a random access scenario, our proposed video codec achieves luma BD-rate savings between 32.5% for HDR HLG UHD and 39.6% for SDR UHD over the HEVC (HM software) anchor for different categories of test sequences.

Intra block copy is a prediction technique in intra coding, which has high compression performance for screen content or computer generated videos. Accordingly, this tool has become part of the upcoming video coding standard H.266/VVC (Versatile Video Coding). Intra block copy is analogous to motion-compensated prediction for the usual inter-picture case with the additional constraint that the reference picture is given by the current partially reconstructed picture. Moreover, the entropy coding of the displacement information of the reference block is carried out in the same way as in inter-picture motion compensation. This publication proposes a set of region-based predictors to improve the current intra block copy approach. The proposed method achieves up to -3.81% of Bjøntegaard-Delta bit-rate saving on top of the existing intra block copy for an all-intra picture configuration.

The upcoming Versatile Video Coding (VVC) Standard includes various new intra prediction tools that were not present in its predecessor High Efficiency Video Coding (HEVC), such as the wide angle intra prediction, the position dependent prediction combination or the multiple reference line intra prediction. In order to improve the intra prediction coding efficiency, this paper proposes the usage of the Intra Subpartition (ISP) algorithm. ISP is an updated version of the Line-Based Intra Prediction (LIP) mode that improves the trade-off between coding gain and complexity of the original method. The basic principle of ISP consists in subdividing an intra-predicted block into 2 or 4 subpartitions of at least 16 samples according to the original block dimensions. The method has been implemented on top of the VVC Test Model 3.0 (VTM-3.0), with the result of obtaining a gain of 0.57% with encoding and decoding run-times of 112% and 102% respectively for the All Intra configuration and a gain of 0.29% with encoding and decoding run-times of 102% and 101% respectively for the Random Access configuration.

Versatile Video Coding (VVC) is going to be the successor of High Efficiency Video Coding (HEVC). The new standard (currently under development) requires the adoption of tools that provide a good trade-off between gain and implementation complexity. In previous work we proposed a Line-Based Intra Prediction (LIP) algorithm to improve the coding performance of the upcoming standard. However, that contribution did not sufficiently take into account the hardware-related complexity of the method. For this reason, this publication addresses these problems and proposes several modifications of the algorithm to solve them. Experimental results show an average gain of 1.0% and 0.5% for the All Intra (AI) and Random Access (RA) configurations, respectively.

Intra prediction plays a very important role in current video coding technologies like the H.265/High Efficiency Video Coding (HEVC) standard, the Joint Exploration Test Model (JEM) and the upcoming Versatile Video Coding (VVC) standard. In previous work we proposed a Line-Based Intra Prediction algorithm to improve the state-of-art coding performance of HEVC and JEM. This method divides (horizontally or vertically) a block into lines and then it codes each of them individually in a sequential manner. At the encoder side, however, it is necessary to select an optimal combination of intra mode and 1-D split type in a Rate-Distortion sense. Since testing for every block all possible combinations of these two parameters would imply a very significant increase in the encoder complexity, this paper proposes several fast algorithms to reduce the number of tests and improve the overall trade-off between complexity and gain. The experimental results show a reduction of the encoder run-time from 322% to 166% in exchange for a loss of 0.34% for the All Intra configuration and from 151% to 116% for a loss of 0.15% in the case of Random Access.

Transform coding tools in video coding have traditionally relied on the Discrete Cosine Transform Type II (DCT-II) to map residual signals to a new domain where quantization and entropy coding tools achieve a better coding efficiency than in the spatial domain. However, the DCT-II is not sufficient to model all different types of residual signals efficiently, especially in the intra-predicted blocks case. For this reason, the DST-VII was introduced in H.265/High Efficiency Video Coding (HEVC) in order to improve the compression performance of 4 × 4 intra-predicted blocks. In this paper we propose a multiple core transform approach, in which each transform is separable and generated by combining two one-dimensional transforms for the vertical and horizontal directions. The pair of 1-D transforms is selected from a set of three different types of Discrete Trigonometric Transforms and the Identity Transformation. Test results show that the proposed algorithm achieves bit rate reductions of 3% on average with respect to HEVC for intra-predicted residuals.

Video compression techniques exploit the statistical redundancy present in video signals to efficiently reduce the amount of information sent to the decoder. We contribute with a kernel-based analysis of the residual error blocks. In particular, we borrow dimension reduction techniques from machine learning, namely Principal Component Analysis (PCA) and nonlinear Kernel Principal Component Analysis (KPCA), to assess the spatial structure of block residuals. Interestingly, a nonlinear structure is observed that correlates to the rate-distortion costs of the blocks. Simulations by using a test set of videos with cropped Ultra High Definition (UHD) resolution show interesting results.