Rajan Laxman Joshi

Transform Coefficient Coding in HEVC

This paper describes transform coefficient coding in the draft international standard of High Efficiency Video Coding (HEVC) specification and the driving motivations behind its design. Transform coefficient coding in HEVC encompasses the scanning patterns and coding methods for the last significant coefficient, significance map, coefficient levels, and sign data. Special attention is paid to the new methods of last significant coefficient coding, multilevel significance maps, high-throughput binarization, and sign data hiding. Experimental results are provided to evaluate the performance of transform coefficient coding in HEVC.

Special Section on the Joint Call for Proposals on High Efficiency Video Coding (HEVC) Standardization

The five papers in this special section were among those submitted in response to the joint call for proposals on high efficiency video coding (HEVC) standardization. Although at this point of development it is still unclear which specific elements the final HEVC standard will contain, the selection of the papers was made such that together they would cover most of the promising tools and technologies that seem likely to be included in the standard.

Overview of the Emerging HEVC Screen Content Coding Extension

A screen content coding (SCC) extension to High Efficiency Video Coding (HEVC) is currently under development by the Joint Collaborative Team on Video Coding, which is a joint effort from the ITU-T Video Coding Experts Group and the ISO/IEC Moving Picture Experts Group. The main goal of the HEVC-SCC standardization effort is to enable significantly improved compression performance for videos containing a substantial amount of still or moving rendered graphics, text, and animation rather than, or in addition to, camera-captured content. This paper provides an overview of the technical features and characteristics of the current HEVC-SCC test model and related coding tools, including intra-block copy, palette mode, adaptive color transform, and adaptive motion vector resolution. The performance of the SCC extension is compared against existing standards in terms of bitrate savings at equal distortion.

A Hybrid Video Coder Based on Extended Macroblock Sizes, Improved Interpolation, and Flexible Motion Representation

This paper describes a video coding technology proposal submitted by Qualcomm in response to a joint call for proposals (CfP) issued by ITU-T SG16 Q.6 (VCEG) and ISO/IEC JTC1/SC29/WG11 (MPEG) in January 2010. The proposed video codec follows a hybrid coding approach based on temporal prediction, followed by transform, quantization, and entropy coding of the residual. Some of its key features are extended block sizes (up to 64 × 64), single pass switched interpolation filters with offsets, mode-dependent directional transforms for intra-coding, luma and chroma high precision filtering, geometric motion partitions, adaptive motion vector resolution and efficient 16-point transforms. It also incorporates internal bit-depth increase and modified quadtree-based adaptive loop filtering. Simulation results are presented to demonstrate the high compression efficiency achieved by the proposed video codec at the expense of moderate increase in encoding and decoding complexity compared to the advanced video coding standard (AVC/H.264). For the random access and low delay configurations, it achieved average bit rate reductions of 30.9% and 33.0% for equivalent peak signal-to-noise ratio, respectively, compared to the corresponding AVC anchors. The proposed codec scored highly in both subjective evaluations and objective metrics and was among the best-performing CfP proposals.

Transform coefficient coding in HEVC

ITU-T VCEG and ISO/IEC MPEG have undertaken a joint standardization activity on video coding called High Efficiency Video Coding (HEVC). This paper describes the transform coefficient coding in the HEVC Test Model (WD5) and the motivations driving the design. The coefficient coding description encompasses the scan patterns and the coding methods of the last significant coefficient, significance map and coefficient level. Special focus is given to the method for coding the last significant coefficient in the block.

Efficient large size transforms for high-performance video coding

This paper describes design of transforms for extended block sizes for video coding. The proposed transforms are orthogonal integer transforms, based on a simple recursive factorization structure, and allow very compact and efficient implementations. We discuss techniques used for finding integer and scale factors in these transforms, and describe our final design. We evaluate efficiency of our proposed transforms in VCEGs H.265/JMKTA framework, and show that they achieve nearly identical performance compared to much more complex transforms in the current test model.

Neighboring block based disparity vector derivation for 3D-AVC

3D-AVC, being developed under Joint Collaborative Team on 3D Video Coding (JCT-3V), significantly outperforms the Multiview Video Coding plus Depth (MVC+D) which has no new macroblock level coding tools compared to Multiview video coding extension of H.264/AVC (MVC). However, for multiview compatible configuration, i.e., when texture views are decoded without accessing depth information, the performance of the current 3D-AVC is only marginally better than MVC+D. The problem is caused by the lack of disparity vectors which can be obtained only from the coded depth views in 3D-AVC. In this paper, a disparity vector derivation method is proposed by using the motion information of neighboring blocks and applied along with existing coding tools in 3D-AVC. The proposed method improves 3D-AVC in the multiview compatible mode substantially, resulting in about 20% bitrate reduction for texture coding. When enabling the so-called view synthesis prediction to further refine the disparity vectors, the performance of the proposed method is 31% better than MVC+D and even better than 3D-AVC under the best performing 3D-AVC configuration.

R-D based quantization in H.264

In this paper, a rate-distortion optimized quantization scheme is described with application to H.264 video encoding. An efficient implementation of H.264 macroblock level adaptive quantization parameter selection is also described. Together these two encoder-only changes can achieve on average over 6% bit rate reduction under common testing conditions that are used in the H.264 standardization community. The described techniques provide this improvement in compression capability while retaining conformance of the encoded data to the H.264 standard. Thus, full compatibility with standard decoders can be achieved when applying these techniques.

Color palette for screen content coding

With the prevalence of high speed Internet access, emerging video applications such as remote desktop sharing, virtual desktop infrastructure, and wireless display require high compression efficiency of screen contents. However, traditional intra and inter video coding tools were designed primarily for natural contents. Screen contents have significantly different characteristics compared with nature contents, e.g. sharp edges, less or no noise, which makes those traditional coding tools less sufficient. In this research, a new color palette based video coding tool is presented. Different from traditionally intra and inter prediction that mainly removes redundancy between different coding units, palette coding targets at the redundancy of repetitive pixel values/patterns within the coding unit. In the palette coding mode, a lookup table named palette which maps pixel values into table indices (also called palette indices) is signaled first. Then the mapped indice for a coding unit (which we call index block) are coded with a novel three-mode run-length entropy coding. Some encoder-side optimization for palette coding is also presented in detail in this paper. Simulation has been performed using the common screen content coding test condition defined by JCT-VC and the results show that palette coding can effectively improve screen content coding efficiency for both lossless and lossy scenarios.

Scalable Video Coding Extension for HEVC

This paper describes a scalable video codec that was submitted as a response to the joint call for proposals issued by ISO/IEC MPEG and ITU-T VCEG on HEVC scalable extension. The proposed codec uses a multi-loop decoding structure. Several inter-layer texture prediction methods are employed to remove the inter-layer redundancy. Inter-layer prediction is also used when coding enhancement layer syntax elements such as motion parameter and intra prediction mode, to further reduce bit overhead. Additionally, alternative transforms as well as adaptive coefficients scanning are used to code the prediction residues more efficiently. Experimental results are presented to demonstrate the effectiveness of the proposed scheme. When compared to HEVC single-layer coding, the additional rate overhead for the proposed scalable extension is 1.2% to 6.4% to achieve two layers of SNR and spatial scalability.