tailieunhanh - DIGITAL IMAGE PROCESSING 4th phần 9

Trong giới hạn, như chiều rộng dòng w phương pháp tiếp cận bằng không, gián đoạn biên độ kết quả được gọi là một lợi thế cạnh mái nhà. Liên tục miền, mô hình hai chiều của các cạnh và đường dây cho rằng các gián đoạn biên độ vẫn không đổi trong một khu phố nhỏ trực giao hồ sơ cá nhân cạnh hoặc dòng. | VISUAL TEXTURE DISCRIMINATION 547 a Sand b Grass c Wool d Raffia FIGURE . Brodatz texture fields. . VISUAL TEXTURE DISCRIMINATION A discrete stochastic field is an array of numbers that are randomly distributed in amplitude and governed by some joint probability density 12 13 . When converted to light intensities such fields can be made to approximate natural textures surprisingly well by control of the generating probability density. This technique is useful for generating realistic appearing artificial scenes for applications such as airplane flight simulators. Stochastic texture fields are also an extremely useful tool for investigating human perception of texture as a guide to the development of texture feature extraction methods. In the early 1960s Julesz 14 attempted to determine the parameters of stochastic texture fields of perceptual importance. This study was extended later by Julesz et al. 15-17 . Further extensions of Julesz s work have been made by Pollack 18 548 IMAGE FEATURE EXTRACTION Spatial W J K o--- Operator INDEPENDENT IDENTICALLY DISTRIBUTED ARRAY -o F J K STOCHACTIC TEXTURE ARRAY FIGURE . Stochastic texture field generation model. Purks and Richards 19 and Pratt et al. 13 20 . These studies have provided valuable insight into the mechanism of human visual perception and have led to some useful quantitative texture measurement methods. Figure is a model for stochastic texture generation. In this model an array of independent identically distributed random variables W j k passes through a linear or nonlinear spatial operator O to produce a stochastic texture array F j k . By controlling the form of the generating probability density p W and the spatial operator it is possible to create texture fields with specified statistical properties. Consider a continuous amplitude pixel x0 at some coordinate j k in F j k . Let the set z1 z2 zJ denote neighboring pixels but not necessarily nearest geometric neighbors raster scanned .