ABSTRACT
Maximum a posteriori estimation of Markov random fields (MRFs) is a popular research area in computer vision, and many algorithms have been proposed to deal with these types of problems. The phase-unwrapping problem is modeled as the optimization of MRFs in this research, and the binary algorithm, improved quadratic pseudo-Boolean optimization, is utilized to solve the phase-unwrapping problem. Both the interferometric phases generated from the commonly used computer simulated surfaces and also real terrains are researched in the experimental section, and the unwrapping results are compared. The proposed algorithm achieves unwrapping results comparable to the state-of-the-art unwrapping method but costs less time for large-scale phase images.
ABSTRACT
In an underwater imaging system, a perspective camera is often placed outside a tank or in waterproof housing with a flat glass window. The refraction of light occurs when a light ray passes through the water-glass and air-glass interface, rendering the conventional multiple view geometry based on the single viewpoint (SVP) camera model invalid. While most recent underwater vision studies mainly focus on the challenging topic of calibrating such systems, no previous work has systematically studied the influence of refraction on underwater three-dimensional (3D) reconstruction. This paper demonstrates the possibility of using the SVP camera model in underwater 3D reconstruction through theoretical analysis of refractive distortion and simulations. Then, the performance of the SVP camera model in multiview underwater 3D reconstruction is quantitatively evaluated. The experimental results reveal a rather surprising and useful yet overlooked fact that the SVP camera model with radial distortion correction and focal length adjustment can compensate for refraction and achieve high accuracy in multiview underwater 3D reconstruction (within 0.7 mm for an object of dimension 200 mm) compared with the results of land-based systems. Such an observation justifies the use of the SVP camera model in underwater application for reconstructing reliable 3D scenes. Our results can be used to guide the selection of system parameters in the design of an underwater 3D imaging setup.
ABSTRACT
OBJECTIVE: To observe changes of plasma neuropeptide Y(NPY) level in ascitic patients with decompensated cirrhosis pre- and post-treatment, there fore to understand the correlation of NPY with liver function and ascitic formation. METHODS: NPY plasma levels in 20 patients with decompensated cirrhosis and ascites were detected by radioimmunological assay. RESULTS: Plasma NPY levels in patients with cirrhotic ascites were significantly lower than those in normal subjects(P < 0.01) in spite of the increases of NPY after ascites decreased (P < 0.01), which were still lower than those in normal subjects(P < 0.01). CONCLUSION: Decreased plasma NPY levels are correlated with the severity of liver damage and may be responsible for the changes of hemodynamics and ascitic formation in patients with liver cirrhosis.
