Rate-distortion optimization of a tone mapping with SDR quality constraint for backward-compatible high dynamic range compression
This paper addresses the problem of designing a global tone mapping operator for rate-distortion optimized backward compatible compression of HDR images. We consider a two layer coding scheme in which a base SDR layer is coded with HEVC, inverse tone mapped and subtracted from the input HDR signal to yield the enhancement HDR layer. The tone mapping curve design is formulated as the minimization of the distortion on the reconstructed HDR signal under the constraint of a total rate cost on both layers, while preserving a good quality for the SDR signal. We first demonstrate that the optimum tone mapping function only depends on the rate of the base SDR layer and that the minimization problem can be separated in two consecutive minimization steps. Experimental results show that the proposed tone mapping optimization yields the best trade-off between rate-distortion performance and quality preservation of the coded SDR.