Artifact assessment, generation, and enhancement of video halftones
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With the advancement of display technology, consumers expect high quality display of image and video data. Many viewers are used to watching video content on high definition television and large screens. However, certain display technologies, such as several of those used in portable electronic books, are limited on resources such as the availability of number of bits per pixel (i.e. the bit-depth). Display of good or even acceptable perceptual quality video on these devices is a hard technical problem that a display designer must solve. Video halftoning reduces the number of represented colors or gray levels for display on devices that are unable to render the video at full bit-depth. Bit-depth reduction results in visible spatial and temporal artifacts. The designer would want to choose the halftoning algorithm that reduces these artifacts while meeting the target platform constraints. These constraints include available bit-depth, spatial resolution, computational power, and desired frame rate. Perceptual quality assessment techniques are useful in comparing different video halftoning algorithms that satisfy the constraints. This dissertation develops a framework for the evaluation of two key temporal artifacts, flicker and dirty-window-effect, in medium frame rate binary video halftones generated from grayscale continuous-tone videos. The possible causes underlying these temporal artifacts are discussed. The framework is based on perceptual criteria and incorporates properties of the human visual system. The framework allows for independent assessment of each of the temporal artifacts. This dissertation presents design of algorithms that generate medium frame rate binary halftone videos. The design of the presented video halftone generation algorithms benefits from the proposed temporal artifact evaluation framework and is geared towards reducing the visibility of temporal artifacts in the generated medium frame rate binary halftone videos. This dissertation compares the relative power consumption associated with several medium frame rate binary halftone videos generated using different video halftone generation algorithms. The presented power performance analysis is generally applicable to bistable display devices. This dissertation develops algorithms to enhance medium frame rate binary halftone videos by reducing flicker. The designed enhancement algorithms reduce flicker while attempting to constrain any resulting increase in perceptual degradation of the spatial quality of the halftone frames. This dissertation develops algorithms to enhance medium frame rate binary halftone videos by reducing dirty-window-effect. The enhancement algorithms reduce dirty-window-effect while attempting to constrain any resulting increase in perceptual degradation of the spatial quality of the halftone frames. Finally, this dissertation proposes design of medium frame rate binary halftone video enhancement algorithms that attempt to reduce a temporal artifact, flicker or dirty-window-effect, under both spatial and temporal quality constraints. Temporal quality control is incorporated by using the temporal artifact assessment framework developed in this dissertation. The incorporation of temporal quality control, in the process of reducing flicker or dirty-window-effect, helps establish a balance between the two temporal artifacts in the enhanced video. At the same time, the spatial quality control attempts to constrain any increase in perceptual degradation of the spatial quality of the enhanced halftone frames.