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
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Introduction
A 3D edge detection scheme
Closing 3D edges
Conclusion
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3D edge detectors are issued
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a generalization in 3D of 2D edge detectors
we propose an unified formalism for 3D edge
detection
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recursive filters
tracking/closing algorithm
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Introduction
A 3D edge detection scheme
Closing 3D edges
Conclusion
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Canny演算法
Step1: smoothing,降低雜訊
 Step2:找邊緣,求梯度的強度
 Step3: hysteresis
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Step1: smoothing
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使用Gaussian filter,在Gaussian filter函式中使用到
variance來調整Gaussian filter的值
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Step2:找邊緣,求梯度的強度
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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
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另外利用
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求出梯度方向
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1st Derivative (Gradient)
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Step3: hysteresis
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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.
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Introduction
A 3D edge detection scheme
Closing 3D edges
Conclusion
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It is often very difficult
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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
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Generally it is easier
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extend uncompleted contours than validate true
contours in a noisy edge image
choose high thresholds
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remove false edge points
use a tracking/closing algorithm
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Deriche and Cocquerez
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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
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The implementation of this algorithm is easy
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if an edge point is identified as an extremity the
algorithm is applied recursively to the involved
extremity until a stop condition is verified
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The 3D extension of this algorithm
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applying it on each plane XY, YZ, ZX
adding the three edge images obtained
This can be justified by the assumption
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the intersection of a 3D surface by at least one plane
among XY,YZ and ZX
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it remains some localized information lacks
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cause holes of width 1 along X,Y or Z
To solve this problem
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select the codes corresponding to holes of width 1
2D implementation consists in scanning the image
fill up each identified hole
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Introduction
A 3D edge detection scheme
Closing 3D edges
Conclusion
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We have proposed a 3D edge detection scheme
saving in computational effort is of great
interest
Currently we investigate true 3D closing edge
methods
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