Tone expansion using lighting style aesthetics

Abstract High Dynamic Range (HDR) is the latest video format for display technology and there is a strong industrial effort in deploying an HDR capable ecosystem in the near future. However, most existing video content today are in Standard Dynamic Range (SDR) format and there is a growing necessity to upscale this content for HDR displays. Tone expansion, also known as inverse tone mapping, converts an SDR content into an HDR format using Expansion Operators (EOs). In this paper, we show that current state-of-the-art EOs do not preserve artistic intent when dealing with content of various lighting style aesthetics. Furthermore, we present a series of subjective user studies evaluating user preference for various lighting styles as seen on HDR displays. This study shows that tone expansion of stylized content takes the form of gamma correction and we propose a novel EO that adapts the gamma value to the intended style of the video. However, we also observe that a power function-based expansion technique causes changes in terms of color appearance. To solve this problem, we propose a simple color correction method that can be applied after tone expansion to emulate the intended colors in HDR. We validate our method through a perceptual evaluation against existing methods. In addition to this, our work targets 1000 nits HDR displays and we present a framework aligning our method in conformance with existing SDR standards and the latest HDR TV standards.