1. A non-transitory program storage device comprising instructions stored thereon to cause one or more processors to: obtain a grayscale version of a high dynamic range (HDR) color input image; downsample the grayscale version of the HDR color input image to generate a down-sampled grayscale input image; apply a spatially varying tone mapping operator (SV-TMO) to the down-sampled grayscale input image to generate a down-sampled grayscale output image; determine a global tone mapping operator (G-TMO) according to, at least in part, a Pool-Adjacent-Violators-Algorithm (PAVA); and apply the G-TMO to the grayscale version of the HDR color input image to generate a low dynamic range (LDR) grayscale output image.