Visually Lossless Compression
Electrical & Computer Engineering
Marcellin, Michael W.
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PublisherThe University of Arizona.
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AbstractStereoscopic 3-D has received considerable attention over the last few decades. Since a stereoscopic 3-D pair includes two 2-D images together, the amount of data for an uncompressed stereo image is double compared to that for an uncompressed 2-D image. Thus efficient compression techniques are of paramount importance. However, crosstalk effect is an inherent perceivable problem in current 3-D display technologies. It can lead not only to degradation in the perceived quality of 3-D images, but also to discomfort in some individuals. Correspondingly, when crosstalk occurs, the compression artifacts in a compressed stereo pair can be perceived, despite the fact that such artifacts are imperceptible in individual left and right images. This dissertation proposes a methodology for visually lossless compression of monochrome stereoscopic 3-D images in which crosstalk effect is carefully considered. In the proposed methodology for visually lossless compression of monochrome stereoscopic 3-D images, visibility thresholds are measured for quantization distortion in JPEG2000 to conceal perceivable compression artifacts. These thresholds are found to be functions of not only spatial frequency, but also of wavelet coefficient variance, as well as the gray level in both the left and right images. In order to avoid a daunting number of measurements of visibility thresholds during subjective experiments, a model for visibility thresholds is developed. The left image and right image of a stereo pair are then compressed jointly using the visibility thresholds obtained from the proposed model to ensure that quantization errors in each image are imperceptible to both eyes. This methodology is then demonstrated via a 3-D stereoscopic liquid crystal display (LCD) system with an associated viewing condition. The resulting images are visually lossless when displayed individually as 2-D images, and also when displayed in stereoscopic 3-D mode. In order to have better perceptual quality of stereoscopic 3-D images, hardware based techniques have been used to reduce crosstalk in 3-D stereoscopic display systems. However, crosstalk is still readily apparent in some 3-D viewing systems. To reduce crosstalk remains after hardware crosstalk compensation, a methodology for crosstalk compensation accomplished via image processing is provided in this dissertation. This methodology focuses on crosstalk compensation of 3-D stereoscopic LCD systems in which active shutter glasses are employed. Subjective experiments indicate that crosstalk is a function of not only the pixel intensity in both the left and right channels, but also of spatial location. Accordingly, look-up tables (LUTs) are developed for spatially-adaptive crosstalk compensation. For a given combination of gray levels in the left and right channels at a specific spatial location, the original pixel values are replaced by values contained in the LUTs. The crosstalk in the resulting stereo pair is significantly reduced, resulting in a significant increase in perceptual image quality.
Degree ProgramGraduate College
Electrical & Computer Engineering