Efficient Motion Modelling with Variable-sized blocks from Hierarchical Cuboidal Partitioning

TL;DR

This paper explores the use of variable-sized cuboidal segments for motion modelling in video coding, demonstrating significant bitrate savings by better aligning with object boundaries compared to fixed-sized blocks.

Contribution

It introduces a novel approach of using cuboidal partitioning for motion modelling, improving coding efficiency in scalable video coding.

Findings

Achieved 6.71%-10.90% bitrate savings on 4K videos.

Cuboidal partitioning aligns better with object boundaries.

Enhanced motion modelling with variable-sized segments.

Abstract

Motion modelling with block-based architecture has been widely used in video coding where a frame is divided into fixed-sized blocks that are motion compensated independently. This often leads to coding inefficiency as fixed-sized blocks hardly align with the object boundaries. Although hierarchical block-partitioning has been introduced to address this, the increased number of motion vectors limits the benefit. Recently, approximate segmentation of images with cuboidal partitioning has gained popularity. Not only are the variable-sized rectangular segments (cuboids) readily amenable to block-based image/video coding techniques, but they are also capable of aligning well with the object boundaries. This is because cuboidal partitioning is based on a homogeneity constraint, minimising the sum of squared errors (SSE). In this paper, we have investigated the potential of cuboids in motion modelling against the fixed-sized blocks used in scalable video coding. Specifically, we have constructed motion-compensated current frame using the cuboidal partitioning information of the anchor frame in a group-of-picture (GOP). The predicted current frame has then been used as the base layer while encoding the current frame as an enhancement layer using the scalable HEVC encoder. Experimental results confirm 6.71%-10.90% bitrate savings on 4K video sequences.