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Optimizing Non Constant Luminance into Constant Luminance for High Dynamic Range Video Distribution

To improve compression efficiency, pixels are traditionally represented using a luma and two chroma values. Such a representation aims at separating light from color information. Two methods are usually considered for computing luma values: Non-Constant Luminance (NCL) and Constant Luminance (CL). CL equations have been derived from the luminous efficacy of the used gamut color primaries in the light linear domain. NCL applies the same equations but on perceptually encoded values, thus resulting in lower compression efficiency and hue shifts. However, given the higher hardware complexity for implementing CL, the common operational practice in legacy television distribution is to use NCL. In this paper, our motivation is to derive a new set of equations that provides the compression benefits of CL with the lower complexity of NCL for High Dynamic Range video distribution. Results show that the proposed method increases compression efficiency significantly over the NCL approach while maintaining NCL's cost complexity.