Preface
Producing truly realistic video is widely seen as the holy grail toward further improving the quality of experience for end users of multimedia services. Additionally, numerous professional applications can be made possible only by the use of video signals with properties beyond the widespread, but very limited, parameter space, such as standard dynamic range. Several new approaches have been proposed and often successfully implemented in the history of the applications that use video data. Currently investigated directions include high spatial resolution, high frame rates, wide color gamut and high-bit-depth rendering.
The human visual system is able to perceive a wide range of colors and luminous intensities, as present in outdoor scenes in everyday life, ranging from bright sunshine to dark shadows. However, current traditional imaging technologies cannot capture nor reproduce such a broad range of luminance. The objective of high dynamic range (HDR) imaging is to overcome these limitations, hence leading to more realistic video content and a greatly enhanced user experience.
HDR applied to still images has been an active field of research and development for many years, especially for photography. However, its extension to video content has been considered only recently. Thanks to rapid technological advancements, commercial HDR video cameras and HDR monitors are becoming available. Nevertheless, the effective deployment of HDR video technologies involves redefining common interfaces for end-to-end content delivery, which in turn entails many technical and scientific challenges for both academia and industry.
This book provides an overview of recently researched technological directions for enabling HDR video in key application areas. More specifically, it covers the state of the art, discusses the effectiveness of various techniques, reviews some of the standardization efforts during the time of writing, and explores new research directions.
By providing a broad coverage, including general and advanced topics, the book should be of interest to a large readership with different backgrounds and expectations. Target readers include researchers, students, engineers, practitioners, and managers. This book has been edited with the aim for it to be the first reference on many topics that encompass HDR video, and to be a relevant handbook for those involved or interested in this field.
The aim is to cover numerous aspects required to establish HDR video systems, ranging from content acquisition to display technologies. Although several applications that use HDR video technologies are discussed, the range of topics covered provides a solid base for the establishment of new HDR application areas.
This book is composed of six parts. After an introduction to the background and fundamentals of HDR imaging, Part I addresses the problem of HDR content acquisition and production. Different approaches are described to capture HDR video, including the use of multiple synchronized sensors, spatial multiplexing of the sensor response, merging of multiple images captured with different exposure times, and capturing multiview HDR video. The impact of HDR on cinematographic shooting is also discussed.
Part II considers several aspects of processing for HDR video. In particular, video tone mapping operators are introduced and evaluated. Next, the way visual anomalies can be used to improve realism is studied. Finally, solutions for color management in the context of HDR imaging are described.
Efficient representation and coding of HDR video is another important topic, and is addressed in Part III. An overview of compression techniques for HDR video is given first. Initial standardization activities related to HDR and wide color gamut are then described. Lastly, the JPEG XT standard for still images, which is backward compatible with the JPEG standard, is presented.
To complete the chain of components in HDR video systems, the issue of display is discussed in Part IV. HDR displays are first characterized and modeled. Next, a dual modulation technique for LED-backlit HDR displays is presented.
As stated before, HDR imaging is the key element for further improvement of the end user experience. For this purpose, we dedicate a full part (Part V) to these aspects, discussing topics related to perception and quality of experience. The perceptual behavior of the human visual system in the context of HDR is discussed first, together with how this knowledge can be exploited to design a perceptually accurate imaging pipeline. The concept of quality of experience in the context of HDR is then carefully introduced, with practical methods and use cases to measure it also being provided. Finally, objective measures to predict HDR image and video quality are described as part of an important component of the quality of experience.
To conclude the book, we illustrate how HDR video technology has already impacted some application fields. Part VI provides such an overview, presenting several applications of HDR imaging in the automotive industry, medical imaging, spacecraft imaging, driving simulation, and watermarking.
The Editors