Perceptual Optimization of a Biologically-Inspired Tone Mapping Operator

With the increasing popularity and accessibility of high dynamic range (HDR) photography, tone mapping operators (TMOs) for dynamic range compression and medium presentation are practically demanding. In this paper, we develop a two-stage neural network-based HDR image TMO that is biologically-inspired, computationally efficient, and perceptually optimized. In Stage one, motivated by the physiology of the early stages of the human visual system (HVS), we first decompose an HDR image into a normalized Laplacian pyramid. We then use two lightweight deep neural networks (DNNs) that take this normalized representation as input and estimate the Laplacian pyramid of the corresponding LDR image. We optimize the tone mapping network by minimizing the normalized Laplacian pyramid distance (NLPD), a perceptual metric calibrated against human judgments of tone-mapped image quality. In Stage two, we generate a pseudo-multi-exposure image stack with different color saturation and detail visibility by inputting an HDR image ``calibrated'' with different maximum luminances to the learned tone mapping network. We then train another lightweight DNN to fuse the LDR image stack into a desired LDR image by maximizing a variant of MEF-SSIM, another perceptually calibrated metric for image fusion. By doing so, the proposed TMO is fully automatic to tone map uncalibrated HDR images. Across an independent set of HDR images, we find that our method produces images with consistently better visual quality, and is among the fastest local TMOs.