UBC Theses and Dissertations
Novel backlighting techniques for high dynamic range displays Emmel, Jakob
High dynamic range (HDR) displays use an array of ultra-bright individually tunable light emitting diodes (LEDs) as a backlight for common liquid crystal displays (LCDs). Through local dimming of LEDs, this combination can show images with very bright highlights while maintaining very low luminance values in dark areas. Current HDR displays, however, have limitations associated with displaying images that have spatially uniform luminance levels: a periodic pattern arising from the underlying pattern of the LEDs behind the LCD is perceptible in the image. The effect of new point spread functions (PSF) on the uniformity and contrast of HDR displays was analyzed. A PSF shaped like a certain type of spline could theoretically create a uniform brightness backlight, as well as producing linear and quadratic gradients, while being capable of showing very high contrast. A practical way to produce such a PSF was used to build an experimental device that achieved a non-uniformity of only ±0.8%, while enabling a contrast ratio of 5:1 and 33:1 over distances of one and two unit cell spacings, respectively. The implementation of a third light modulator in HDR displays, in addition to the backlight LEDs and the front liquid crystal display (LCD) was studied: liquid crystal cells were combined with reflective polarizers to act as light valves, either transmitting or reflecting light. In theory, these reflective light modulators are supposed to decrease power consumption through light recycle effects. The power consumption of displays using the two discussed backlights was simulated. It was found that their power consumption is less than that of a common LCD by a factor of 2-5, but it is about 11 percentage points higher than for a standard HDR display. However, the image quality and contrast are improved compared to both state of the art displays. The advantages of the backlight with the new PSF may help to make HDR displays more useful and competitive in a wide range of applications requiring faithful luminance rendering such as discerning consumer markets, medical imaging, and motion picture editing.
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