IMPROVED TONE MAPPING OPERATOR FOR HDR CODING OPTIMIZING THE DISTORTION/SPATIAL COMPLEXITY TRADE-OFF

A common paradigm to code high dynamic range (HDR) im-age/video content is based on tone-mapping HDR pictures to low dynamic range (LDR), in order to obtain backward com-patibility and use existing coding tools, and then use inverse tone mapping at the decoder to predict the original HDR sig-nal. Clearly, the choice of a proper tone mapping is essential in order to achieve good coding performance. The state-of-the-art to design the optimal tone mapping operator (TMO) minimizes the mean-square-error distortion between the orig-inal and the predicted HDR image. In this paper, we argue that this is suboptimal in rate-distortion sense, and we pro-pose a more effective TMO design strategy that takes into ac-count also the spatial complexity (which is a proxy for the bitrate) of the coded LDR image. Our results show that the proposed optimization approach enables to obtain substantial coding gain with respect to the minimum-MSE TMO. Index Terms — High dynamic range; coding; convex op-timization; spatial complexity. 1