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UBC Theses and Dissertations

Improving perceptual quality of high dynamic range video Azimi Hashemi, Maryam

Abstract

With the real-life viewing experience of High Dynamic Range (HDR) videos and the growing availability of HDR displays and video content, an efficient HDR video delivery pipeline is required for applications such as broadcasting. The existing pipeline has been designed for Standard Dynamic Range (SDR) signals and displays. Using this pipeline for HDR content will result in visible quality degradation as HDR bears fundamental differences with SDR technology such as higher brightness levels and a wider color gamut (WCG). As a result, various HDR delivery pipelines are under development, supporting varying bitrates and visual quality. In this thesis, we improve the visual quality and hence quality of experience (QoE) of delivered HDR videos without increasing the bitrate. First, we investigate the existing transmission pipelines’ efficiency in delivering HDR through an extensive set of subjective experiments. The unprecedented analysis of each pipeline presented in this work, while considering their backward compatibility with SDR displays, provides valuable information for broadcasters to identify the most efficient pipeline in terms of required bitrate and visual quality for viewers. Next, we evaluate the effect that the identified HDR delivery pipeline has color accuracy. These evaluations are helpful to determine the colors that need improvement. By considering certain characteristics of the human visual system (HVS), we propose two processing techniques that improve the perceptual fidelity of these colors. The proposed techniques are shown to outperform the existing methods in terms of maintaining the color information of HDR signals first subjectively through a set of visual evaluations and second objectively by using color difference evaluation metrics. Additionally, for cases where delivered HDR signals are received by an SDR display, we propose two novel color mapping methods that result in the least perceptual color differences compared to the original HDR signal. The proposed color mapping techniques are compatible with the current pipeline infrastructure with minimal implementation cost. The presented work in this thesis improves the visual quality of transmitted HDR videos, either viewed directly on HDR displays or through a mapping process on SDR displays, while the transmission bitrate is not affected.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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