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UBC Theses and Dissertations

Inverse tone mapping of standard dynamic range content for high dynamic range applications Mohammadi, Pedram


High Dynamic Range (HDR) technology has revolutionized the field of digital media, affecting different aspects such as capturing, compression, transmission and display. By modeling the behavior of Human Visual System (HVS) when perceiving brightness and color, HDR technology offers a life-like viewing experience that is far superior to what Standard Dynamic Range (SDR) technology could achieve. While HDR technology has a disruptive impact in different fields, it also opens new revenue sources for SDR content owners and broadcasters that will continue producing real-time events in SDR format for the near future. For the latter case, SDR content need to be efficiently converted to HDR format, taking advantage of the superior visual quality of HDR displays. Over the years, several attempts aimed at converting SDR content to HDR format, a process known as inverse Tone Mapping (iTM). The design of inverse Tone Mapping Operators (iTMOs) is considered a difficult task, as it tries to expand the brightness and color information to ranges not originally captured by SDR cameras. In this thesis, we propose novel iTMOs that can effectively deal with all types of SDR content from dark, to normal and bright scenes, producing high visual quality HDR content. Our proposed methods work in the perceptual domain, which allows us to take advantage of the sensitivity of the human eye to brightness changes in different areas of the scene during the mapping process. To preserve the overall artistic impression, we developed methods that divide the SDR frame into dark, normal (average brightness), and bright regions, allowing us to keep intact dark and bright areas, without darkening or brightening up the frame. We also address the issue of the color shift in SDR to HDR mapping by proposing a perception-based color adjustment method that preserves the hue of colors with insignificant changes in brightness, producing HDR colors that are faithful to their SDR counterparts. Subjective and objective evaluations have shown that our proposed iTMOs outperform the state-of-the-art methods in terms of overall visual quality of the generated HDR video and generating HDR colors that closely follow their SDR counterparts.

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