On the Effectiveness of Video Recolouring as an Uplink-model Video Coding Technique
Date
2021-09-28
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-1631-1746
Type
Thesis
Degree Level
Masters
Abstract
For decades, conventional video compression formats have advanced via incremental improvements with
each subsequent standard achieving better rate-distortion (RD) efficiency at the cost of increased encoder
complexity compared to its predecessors. Design efforts have been driven by common multi-media use cases
such as video-on-demand, teleconferencing, and video streaming, where the most important requirements are
low bandwidth and low video playback latency. Meeting these requirements involves the use of computa-
tionally expensive block-matching algorithms which produce excellent compression rates and quick decoding
times.
However, emerging use cases such as Wireless Video Sensor Networks, remote surveillance, and mobile
video present new technical challenges in video compression. In these scenarios, the video capture and
encoding devices are often power-constrained and have limited computational resources available, while the
decoder devices have abundant resources and access to a dedicated power source. To address these use cases,
codecs must be power-aware and offer a reasonable trade-off between video quality, bitrate, and encoder
complexity. Balancing these constraints requires a complete rethinking of video compression technology.
The uplink video-coding model represents a new paradigm to address these low-power use cases, providing
the ability to redistribute computational complexity by offloading the motion estimation and compensation
steps from encoder to decoder. Distributed Video Coding (DVC) follows this uplink model of video codec
design, and maintains high quality video reconstruction through innovative channel coding techniques. The
field of DVC is still early in its development, with many open problems waiting to be solved, and no defined
video compression or distribution standards. Due to the experimental nature of the field, most DVC codec
to date have focused on encoding and decoding the Luma plane only, which produce grayscale reconstructed
videos.
In this thesis, a technique called “video recolouring” is examined as an alternative to DVC. Video recolour-
ing exploits the temporal redundancies between colour planes, reducing video bitrate by removing Chroma
information from specific frames and then recolouring them at the decoder.
A novel video recolouring algorithm called Motion-Compensated Recolouring (MCR) is proposed, which
uses block motion estimation and bi-directional weighted motion-compensation to reconstruct Chroma planes
at the decoder. MCR is used to enhance a conventional base-layer codec, and shown to reduce bitrate by
up to 16% with only a slight decrease in objective quality. MCR also outperforms other video recolouring
algorithms in terms of objective video quality, demonstrating up to 2 dB PSNR improvement in some cases.
Description
Keywords
Video compression, motion-based video recolouring
Citation
Degree
Master of Science (M.Sc.)
Department
Computer Science
Program
Computer Science