Tham khảo tài liệu 'digital filters part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5 New Design Methods for Two-Dimensional Filters Based on 1D Prototypes and Spectral Transformations Radu Matei Technical University of Iasi Romania 1. Introduction The field of two-dimensional filters and their design methods have been approached by many researchers for more than three decades Lim 1990 Lu Antoniou 1992 . A commonly-used design technique for 2D filters is to start from a specified 1D prototype filter and transform its transfer function using various frequency mappings in order to obtain a 2D filter with a desired frequency response. These are essentially spectral transformations from s to z plane via bilinear or Euler transformations followed by z to z1 z2 mappings approached in early reference papers Pendergrass et al. 1976 Hirano Aggarwal 1978 Harn Shenoi 1986 . Generally these spectral transformations conserve stability so from 1D prototypes various stable recursive 2D filters can be obtained. There are several classes of filters with orientation-selective frequency response useful in some image processing tasks such as edge detection motion analysis etc. An important class are the steerable filters synthesized as a linear combination of a set of basis filters Freeman Adelson 1991 . Another important category are Gabor filters with applications in some complex tasks in image processing. A major reference on oriented filters is Chang Aggarwal 1977 where a technique for rotating the frequency response of separable filters is developed. The proposed method considers transfer functions in rational powers of z and realized by input-output signal array interpolations. Anisotropic in particular elliptically-shaped filters have also been studied extensively and are used in some interesting applications . in remote sensing for directional smoothing applied to weather images Lakshmanan 2004 also in texture segmentation and pattern recognition. Other directionally selective operators are proposed in Danielsson 1980 . Another particular class .