Browsing by Author "Dorney, Timothy D."
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Item Edge Localized Image Sharpening via Reassignment with Application to Computed Tomography(2000-07-01) Dorney, Timothy D.; Bhashyam, Srikrishna; Doran, Andrew; Choi, Hyeokho; Flandrin, Patrick; Baraniuk, Richard G.; Center for Multimedia Communications (http://cmc.rice.edu/); Digital Signal Processing (http://dsp.rice.edu/)Traditional filtering methods operate on the entire signal or image. In some applications, however, errors are concentrated in specific regions or features. A prime example is images generated using computed tomography. Practical implementations limit the amount of high frequency content in the reconstructed image, and consequently, edges are blurred. We introduce a new post-reconstruction edge enhancement algorithm, based on the reassignment principle and wavelets, that localizes its sharpening exclusively to edge features. Our method enhances edges without disturbing the low frequency textural details.Item Imaging with Terahertz Pulses(2000-07-01) Dorney, Timothy D.; Johnson, Jon L.; Mittleman, Daniel M.; Baraniuk, Richard G.; Center for Multimedia Communications (http://cmc.rice.edu/); Digital Signal Processing (http://dsp.rice.edu/)Recently, a real-time imaging system based on terahertz (THz) time-domain spectroscopy has been developed. This technique offers a range of unique imaging modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the THz pulses. This paper provides a brief introduction of the state-of-the art in THz imaging. It also focuses on expanding the potential of this new and exciting field through two major efforts. The first concentrates on improving the experimental sensitivity of the system. We are exploring an interferometric arrangement to provide a background-free reflection imaging geometry. The second applies novel digital signal processing algorithms to extract useful information from the THz pulses. The possibility exists to combine spectroscopic characterization and/or identification with pixel-by-pixel imaging. We describe a new parameterization algorithm for both high and low refractive index materials.Item Imaging with THz Pulses(2000-09-01) Dorney, Timothy D.; Johnson, Jon L.; Mittleman, Daniel M.; Baraniuk, Richard G.; Digital Signal Processing (http://dsp.rice.edu/)A real-time imaging system based on terahertz (THz) time-domain spectroscopy has been demonstrated. This technique offers a range of unique imaging modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the THz pulses. This paper provides an introduction of the state-of-the art in THz imaging. It also focuses on expanding the potential of this new and exciting field through two major efforts. The first concentrates on improving the experimental sensitivity of the system. We are exploring an interferometric arrangement to provide a background-free reflection imaging geometry. The second applies novel digital signal processing algorithms to extract useful information from the THz pulses. The possibility exists to combine spectroscopic characterization and/or identification with pixel-by-pixel imaging.Item Spectroscopic Imaging using Terahertz Time-Domain Signals(2000-04-01) Dorney, Timothy D.; Baraniuk, Richard G.; Mittleman, Daniel M.; Digital Signal Processing (http://dsp.rice.edu/)Imaging systems based on terahertz time-domain spectroscopy offer a range of unique modalities due to the broad bandwidth, sub-picosecond duration, and phase-sensitive detection of the terahertz pulses. Furthermore, an exciting possibility exists to combine spectroscopic characterization and/or identification with imaging because the radiation is broadband in nature. In order to achieve this, novel methods for real-time analysis of terahertz waveforms are required. Unfortunately, both the absorption and the phase delay of a transmitted terahertz pulse vary exponentially with the sample's thickness. We describe a robust algorithm for extracting both the thickness and the complex index of refraction of an unknown sample. In contrast, most spectroscopic transmission measurements require accurate knowledge of the sample's thickness to determine the optical parameters. We also investigate the limits of our method.Item Terahertz Multistatic Reflection Imaging(2002-07-01) Dorney, Timothy D.; Symes, William; Baraniuk, Richard G.; Mittleman, Daniel M.; Digital Signal Processing (http://dsp.rice.edu/)We describe a new imaging method using single-cycle pulses of terahertz (THz) radiation. This technique emulates the data collection and image processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a migration procedure to solve the inverse problem; this permits us to reconstruct the location, the shape, and the refractive index of targets. We show examples for both metallic and dielectric model targets, and we perform velocity analysis on dielectric targets to estimate the refractive indices of imaged components. These results broaden the capabilities of THz imaging systems and also demonstrate the viability of the THz system as a test bed for the exploration of new seismic processing methods.Item Terahertz Reflection Imaging using Kirchhoff Migration(2001-10-01) Dorney, Timothy D.; Johnson, Jon L.; Rudd, J. Van; Baraniuk, Richard G.; Symes, William; Mittleman, Daniel M.; Digital Signal Processing (http://dsp.rice.edu/)We describe a new imaging method that uses single-cycle pulses of terahertz (THz) radiation. This technique emulates data-collection and image-processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a simple migration procedure to solve the inverse problem; this permits us to reconstruct the location and shape of targets. These results demonstrate the feasibility of the THz system as a test-bed for the exploration of new seismic processing methods involving complex model systems.