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UBC Theses and Dissertations

Tone-mapping high dynamic range images and videos for bit-depth scalable coding and 3D displaying Mai, Zicong


High dynamic range (HDR) images and videos provide superior picture quality by allowing a larger range of brightness levels to be captured and reproduced than their traditional 8-bit low dynamic range (LDR) counterparts. Even with existing 8-bit displays, picture quality can be significantly improved if the content is first captured in HDR format and then converted to LDR format. This converting process is called tone-mapping. In this thesis, we address different aspects of tone-mapping. HDR video formats are unlikely to be broadly accepted without the backward-compatibility with LDR devices. We first consider the case where only the tone-mapped LDR content is transmitted and the HDR video is reconstructed at the receiver by inversely tone-mapping the encoded-decoded LDR video. We show that the appropriate choice of a tone-mapping operator can result in a reconstructed HDR video with good quality. We develop a statistical model of the distortion resulting from tone-mapping, compressing, de-compressing and inverse tone-mapping the HDR video. This model is used to formulate an optimization problem that finds the tone-curve that minimizes the distortion in the reconstructed HDR video. We also derive a simplified version of the model that leads to a closed-form solution for the optimization problem. Next, we consider the case where the HDR content is transmitted using an LDR and an enhancement layers. We formulate an optimization problem that minimizes the transmitted bit-rate of a video sequence and also results in the tone-mapped video that satisfies some desired perceptual appearance. The problem formulation also contains a constraint that suppresses temporal flickering artifacts. We also propose a technique that tone-maps an HDR video directly in a compression friendly color space (e.g., YCbCr) without the need to convert it to the RGB domain. We study the design of 3D HDR-LDR tone-mapping operators. To find the appropriate tone-mapping characteristics that contribute to good 3D representation, subjective psychophysical experiments are performed for i) evaluating existing tone-mapping operators on 3D HDR images and ii) investigating how the preferred level of brightness and details differ between 3D and 2D images. The results are analyzed to find out the desired attributes.

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