Preface

Visual compression has been a very active field of research and development for over 20 years, leading to many different compression systems and to the definition of international standards. There is likely to be a continued need for better compression efficiency, as video content becomes increasingly ubiquitous and places unprecedented pressure on upcoming new applications in the future. At the same time, the challenge of handling ever more diverse content coded in a wide variety of formats makes reconfigurable coding a potentially useful prospect.

This book aims to bring together selected recent advances, applications and some original results in the area of image and video compression. They can be useful for researchers, engineers, graduate and postgraduate students, experts in this area and hopefully also for people interested generally in computer science, video coding and video quality.

Regarding the organization of the book, it is divided into three parts having seven chapters in total. Chapters are clustered into compression, motion estimation and quality.

The first chapter presents a review of techniques proposed compressed sensing. Compressive Sensing is a new field and its application to video systems is even more recent. There are many avenues for further research and thorough quantitative analyses are still lacking. Number of encoding strategies that has been adopted is described.

Chapter two analyses the transcoding framework for video communications between mobile devices. In addition, it is proposed a WZ to H.264/AVC transcoder designed to support mobile-to-mobile video communications. Since the transcoder device accumulates the highest complexity from both video coders, reducing the time spent in this process is an important goal. This chapter also presents two approaches to speed-up WZ decoding and H.264/AVC encoding.

Chapter three presents a few evaluations and analysis that characterize the loss in perceived interpretability of motion imagery arising from various compression methods and compression rates. Evaluation of image compression for motion imagery illustrates how interpretability-based methods can be applied to the analysis of the

#### XII Preface

image chain. The chapter also presents both objective image metrics and analysts' assessments of various compressed products.

Chapter four presents an overview of H.264 motion estimation and its types and also the various estimation criterions that decides the complexity of the chosen algorithm.

Chapter five is a systematic review of the pixel domain based global motion estimation approaches. The chapter discusses shortcomings in noise filtering and computational cost, the improvement approaches including hierarchical global motion estimation, partial pixel set based global motion estimation and compressed domain based global motion estimation are provided. Four global motion based applications including GMC/LMC in MPEG-4 video coding standard, global motion based sport video shot classification, GM/LM based error concealment and text occluded region recovery are described in this chapter.

Chapter six argues that exploiting saliency-based video compression is a challenging and exciting area of research and especially nowadays when saliency models include more and more top-down information and manages to better and better predict real human gaze. Multimedia applications are a continuously evolving domain and compression algorithms must also evolve and adapt to new applications. The explosion of portable devices with less bandwidth and smaller screens, but also the future semantic TV/web and its object-based description will lead in the future to a higher importance of saliencybased algorithms for multimedia data repurposing and compression.

The large amount of studies developed for this purpose related to quality assessment gives a general idea about the importance of this theme in video compression. The evolution of metrics and techniques is constant, finding the best ways of evaluating the quality of video sequences.

Chapter seven describes a state of the art in quality assessment and techniques of subjective and objective assessment, with the most common artefacts and impairments derived from compression and transmission.

I wish to thank all the authors who have contributed to this book. I hope that by reading this book you will get many useful ideas for your own research, which will help to bridge the gap between video compression technology and applications.

I also hope this book is enjoyable to read and will further contribute to video compression, which requires a further interest and attention in both research and application fields.

#### **Dr Amal Punchihewa**

**Part 1** 

**Compression** 

PhD, MEEng, BSC(Eng)Hons, CEng, FIET, MIPENZ, MIEEE, MSLAAS , MCS, Leader - Multi-Media Research Group, The School of Engineering and Advanced Technology, Massey University (Turitea), New Zealand
