Report

Author: Monga, O.; Deriche, R.; Malandain, G.; Cocquerez, J.P. Source: Pattern Recognition, 1990. Proceedings., 10th International Conference , Page(s): 652 - 654 Student: Jia – Hong Chen Advisor: Ku – Yaw Chang 2010/05/06 1 Introduction A 3D edge detection scheme Closing 3D edges Conclusion 2010/05/06 2 3D edge detectors are issued a generalization in 3D of 2D edge detectors we propose an unified formalism for 3D edge detection 2010/05/06 recursive filters tracking/closing algorithm 3 Introduction A 3D edge detection scheme Closing 3D edges Conclusion 2010/05/06 4 Canny演算法 Step1: smoothing,降低雜訊 Step2:找邊緣,求梯度的強度 Step3: hysteresis 2010/05/06 5 Step1: smoothing 2010/05/06 使用Gaussian filter,在Gaussian filter函式中使用到 variance來調整Gaussian filter的值 6 2010/05/06 7 2010/05/06 8 2010/05/06 9 Step2:找邊緣,求梯度的強度 使用Sobel method找出邊緣,他會先計算出每一個像素 的值再利用 求出梯度 另外利用 2010/05/06 求出梯度方向 10 1st Derivative (Gradient) 2010/05/06 11 2010/05/06 12 2010/05/06 13 2010/05/06 14 2010/05/06 15 Step3: hysteresis 2010/05/06 設定2個門檻值T1和T2,由G得到的結果,任何像素如果 大於T1則被認定為邊緣像素,而在這個邊緣像素鄰近的 點如果有大於T2也會被認定為邊緣像素. 16 Introduction A 3D edge detection scheme Closing 3D edges Conclusion 2010/05/06 17 It is often very difficult 2010/05/06 select adequate thresholds for the thresholding stage High thresholds allows to remove noisy edge points but also true edge points low thresholds allow to obtain all true edge points but also noisy edge points 18 Generally it is easier extend uncompleted contours than validate true contours in a noisy edge image choose high thresholds 2010/05/06 remove false edge points use a tracking/closing algorithm 19 Deriche and Cocquerez 2D edge closing method proposed supposes that it is possible to recognize endpoints of contours Examination of a neighbourhood 3 x 3 of an edge point The implementation of this algorithm is easy 2010/05/06 if an edge point is identified as an extremity the algorithm is applied recursively to the involved extremity until a stop condition is verified 20 The 3D extension of this algorithm applying it on each plane XY, YZ, ZX adding the three edge images obtained This can be justified by the assumption 2010/05/06 the intersection of a 3D surface by at least one plane among XY,YZ and ZX 21 it remains some localized information lacks cause holes of width 1 along X,Y or Z To solve this problem 2010/05/06 select the codes corresponding to holes of width 1 2D implementation consists in scanning the image fill up each identified hole 22 Introduction A 3D edge detection scheme Closing 3D edges Conclusion 2010/05/06 23 We have proposed a 3D edge detection scheme saving in computational effort is of great interest Currently we investigate true 3D closing edge methods 2010/05/06 24 2010/05/06 25