Improved tone mapping operator for HDR coding optimizing the distortion/spatial complexity trade-off

A common paradigm to code high dynamic range (HDR) image/video content is based on tone-mapping HDR pictures to low dynamic range (LDR), in order to obtain backward compatibility and use existing coding tools, and then use inverse tone mapping at the decoder to predict the original HDR signal. 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 original and the predicted HDR image. In this paper, we argue that this is suboptimal in rate-distortion sense, and we propose a more effective TMO design strategy that takes into account 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.