Perceptual Uniformity for High-Dynamic-Range Television Systems

Abstract

High dynamic range (HDR) television promises a qualitatively better viewing experience, but to fully realize its potential and to achieve consistent high quality images, the psychovisual aspects of human vision must be taken into account. This paper reviews the nonlinearities inherent in conventional standard dynamic range (SDR) television and discusses how these are required to accommodate psychovisual effects. The thresholds at which changes in brightness can be detected, embodied in Weber's and De Vries-Rose's laws, are discussed in the context of the need to minimize “banding” artifacts due to quantization. This effect also provides a simple psychovisual definition for the dynamic range of video. The second important psychovisual effect considered is that of surround brightness on the perception of emissive images in dim or dark surroundings. This effect is accommodated by implementing an overall system nonlinearity, the rendering intent, which is typically a gamma (power law) function. The appropriate gamma exponent is considered in special cases and interpolated to provide a general formula. Based on these psychovisual effects, an HDR television system is proposed that supports the highest quality HDR images with a simultaneous dynamic range substantially beyond the limits of the human visual system in a single adaptation state. It is defined by a single opto-electronic transfer function (OETF), with a variable display electro-optic transfer function (EOTF) to accommodate the eye's adaptation. It is also compatible with existing, SDR, displays and infrastructure and requires no metadata.