TAILIEUCHUNG - Recent Advances in Signal Processing 2011 Part 2

Tham khảo tài liệu 'recent advances in signal processing 2011 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 22 Recent Advances in Signal Processing interest of the combination of DIRECT with spline interpolation comes from the elevated computational load of DIRECT. Details about DIRECT algorithm are available in Jones et al. 1993 . Reducing the number of unknown values retrieved by DIRECT reduces drastically its computational load. Moreover in the considered application spline interpolation between these node values provides a continuous contour. This prevents the pixels of the result contour from converging towards noisy pixels. The more interpolation nodes the more precise the estimation but the slower the algorithm. After considering linear and nearly linear contours we focus on circular and nearly circular contours. 4. Star-shape contour retrieval Star-shape contours are those whose radial coordinates in polar coordinate system are described by a function of angle values in this coordinate system. The simplest star-shape contour is a circle centred on the origin of the polar coordinate system. Signal generation upon a linear antenna yields a linear phase signal when a straight line is present in the image. While expecting circular contours we associate a circular antenna with the processed image. By adapting the antenna shape to the shape of the expected contour we aim at generating linear phase signals. Problem setting and virtual signal generation Our purpose is to estimate the radius of a circle and the distortions between a closed contour and a circle that fits this contour. We propose to employ a circular antenna that permits a particular signal generation and yields a linear phase signal out of an image containing a quarter of circle. In this section center coordinates are supposed to be known we focus on radius estimation center coordinate estimation is explained further. Fig. 3 a presents a binary digital image I. The object is close to a circle with radius value r and center coordinates lc mc . Fig. 3 b shows a sub-image extracted from the original image

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