HIGH DYNAMIC RANGE, VISUAL ADAPTATION, AND CONSUMER PERCEPTION: APPLYING VISUAL SCIENCE IN THE SEARCH FOR CONSENSUS ON HDR

摘要

As momentum builds in the market transition to 4k Ultra HD, the emergence of High Dynamic Range (HDR) technology is drawing video engineers' attention to new issues that must be resolved if the full potential of a next-generation viewing experience is to be realized. While 4k UHD provides the pixel density essential to enabling an immersive, big-screen TV viewing experience, HDR represents an opportunity to deliver a level of realism on video displays of all sizes that is far beyond what has been possible until now. By delivering greater contrast, increased luminance and an expanded color gamut, HDR vastly surpasses the SDR (Standard Dynamic Range) parameters that were standardized with ratification of Recommendation ITU-R BT. 7091 25 years ago. Unlike 4k UHD, which has been a fairly straight-forward step in the evolution of display resolution built on the SDR foundation, HDR introduces a new paradigm where the dimensions of the new viewing experience must be defined in keeping with basic principles of the human visual response system. This will impact everything that's done in the creation and dissemination of video content from initial capture through production, post production, and processing for distribution. Presently there are a number of approaches to HDR vying for traction in the marketplace. Much of the modeling that has gone into setting their parameters has focused on human contrast sensitivity, often in the context of non-broadcast use cases such as cinematic and episodic TV programming. However, as various organizations pursue HDR standardization initiatives to facilitate market adoption, the priority must be on choosing solutions from a much broader perspective on visual response processes. Along with responsiveness to degrees of contrast, developers must consider human perceptual factors such as: Light and dark adaptation; Brightness sensitivity; Reaction to ambient light; How color is perceived under different Conditions; Responses to frame-rate flicker that might be introduced with expansions in dynamic range. Moreover, planning for HDR must take into account the live TV broadcast environment. Content producers and distributors will have to determine how human visual response in the HDR environment will impact quality parameters for advertising, channel changes between HDR and SDR programming and the presentation of user interfaces, captioning and other textual and graphic elements. The impact of various HDR modes on bitrate and bandwidth requirements will also be an important consideration, especially for MVPDs.