Rate distortion optimized tone curve for high dynamic range compression

In this paper, we define a reversible tone mapping-operator (TMO) for efficient compression of High Dynamic Range (HDR) images using a Low Dynamic Range (LDR) encoder. In our compression scheme, the HDR image is tone mapped and encoded. The inverse tone curve is also encoded, so that the decoder can reconstruct the HDR image from the LDR version. Based on a statistical model of the encoder error and assumptions on the rate of the encoded LDR image, we find a closed form solution for the optimal tone curve with respect to the rate and the mean square error (MSE) of the reconstructed HDR image. It is shown that the proposed method gives superior compression performance compared to existing tone mapping operators.