Abstract

In the past decade, the development of transform coding techniques has achieved significant progress and several advanced transform tools have been adopted in the new generation Versatile Video Coding (VVC) standard. In this paper, a brief history of transform coding development during VVC standardization is presented, and the transform coding tools in the VVC standard are described in detail together with their initial design, incremental improvements and implementation aspects. To improve coding efficiency, four new transform coding techniques are introduced in VVC, which are namely Multiple Transform Selection (MTS), Low-Frequency Non-separable Secondary Transform (LFNST) and Sub-Block Transform (SBT), as well as a large (64-point) type-2 DCT. The experimental results on VVC reference software (VTM-9.0) show that average 4.5% and 3.6% overall coding gain can be achieved by the VVC transform coding tools for All Intra and Random Access configurations, respectively.

Highlights

  • T RANSFORM coding has been an essential part of many practical video codecs for achieving a high compression ratio, and it has been successfully adopted in multiple video coding standards, e.g., H.261 [1], MPEG-1 [2], MPEG-2 [3], H.263 [4], H.264/AVC [5] and High-Efficiency Video Coding (HEVC) [6]

  • Under the first-order Markov conditions, which efficiently model the characteristics of natural imagery sources, it has been mathematically proved that DCT-2 approximates the optimal data-driven Karhunen-Loève transform (KLT) [8]

  • This paper provides a history of the tool development in transform coding and presents how these tools are shaped into their final designs in Versatile Video Coding (VVC)

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Summary

INTRODUCTION

T RANSFORM coding has been an essential part of many practical video codecs for achieving a high compression ratio, and it has been successfully adopted in multiple video coding standards, e.g., H.261 [1], MPEG-1 [2], MPEG-2 [3], H.263 [4], H.264/AVC [5] and High-Efficiency Video Coding (HEVC) [6]. From the industrial standardization side, the Joint Video Exploration Team (JVET) was created in 2015 as a joint effort of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11 to explore advanced video coding technologies beyond HEVC. This paper provides a history of the tool development in transform coding and presents how these tools are shaped into their final designs in VVC.

Primary Transform
Secondary Transform
Transform Partitioning
TRANSFORM DESIGN IN VVC
Encoder Decision for MTS and LFNST
COMPLEXITY ANALYSIS
Coding Efficiency
Tool Analysis
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