3D edge detection by separable recursive filtering and edge closing

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3D EDGE DETECTION BY SEPARABLE RECURSIVE

FILTERING AND EDGE CLOSING

2010/05/06

Author: Monga, O.; Deriche, R.; Malandain, G.; Cocquerez, J.P.Source: Pattern Recognition, 1990. Proceedings., 10th International Conference , Page(s): 652 - 654Student: Jia – Hong ChenAdvisor: Ku – Yaw Chang

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Outline

Introduction A 3D edge detection scheme Closing 3D edges Conclusion

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Introduction

3D edge detectors are issued a generalization in 3D of 2D edge detectors

we propose an unified formalism for 3D edge detection recursive filters tracking/closing algorithm

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Outline


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A 3D edge detection scheme

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 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

另外利用求出梯度方向

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1st Derivative (Gradient)

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Step3: hysteresis 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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Outline


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Closing 3D edges

It is often very difficult 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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Closing 3D edges

Generally it is easier extend uncompleted contours than validate

true contours in a noisy edge image choose high thresholds

remove false edge points use a tracking/closing algorithm

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Closing 3D edges

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 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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Closing 3D edges

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 the intersection of a 3D surface by at least

one plane among XY,YZ and ZX

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Closing 3D edges

it remains some localized information lacks cause holes of width 1 along X,Y or Z

To solve this problem 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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Outline


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Conclusion

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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The End

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3D edge detection by separable recursive filtering and edge closing

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