Approaches to high dynamic range video

The television industry is excited about high dynamic range (HDR) video and its potential for dramatic improvements in picture quality. Together with wide colour gamut, brighter displays and ultra-high definition resolution, HDR represents a fundamental change in television which is, arguably, the biggest change since the development of colour television. This paper considers emerging approaches to high dynamic range video. Two complementary approaches are the focus of standardisation efforts in organisations such as the International Telecommunication Union (ITU) in ITU-R SG6 and VCEG/JCTVC/MPEG. The Hybrid Log-Gamma (HLG) approach is "scene referred", where the video signal represents light captured by a camera. The alternative approach to television, called Perceptual Quantisation (PQ), is "display referred", where the signal represents light emitted by a reference display. This paper contrasts the HLG and PQ approaches to HDR video. It describes the role of non-linearities within the TV system. The opto-electronic transfer function (OETF) and the electro-optical transfer function (EOTF), implemented within camera and display respectively, minimise the number of bits required for an in fixed point video format. The opto-optical transfer function (OOTF) is a psychovisual adjustment to ensure perceptually consistent images. New experimental results are presented that show how the gamma exponent of a power function OOTF should vary with peak display luminance. The importance of applying OOTF to the luminance in HDR video is also considered.