應用灰階共變異矩陣之多重指標於瑕疵檢測

Eigenvalue-based similarity measures and their applications for defect inspection

楊榮華(Ron-Hwa Yang)

指導教授 ： 蔡 篤 銘

元智大學/工程學院/工業工程與管理學系/碩士(2002年)

摘要

現階段工業檢測的趨勢，已由傳統人工檢測進入應用機器視覺於自動化檢測，傳統人工檢測有訓練不良、素質不一的缺點，為解決人工檢測的缺失，以自動化檢測技術來取代傳統人工檢測方式，並廣泛應用於醫學、電子產業、航空工業領域，皆應用自動檢測技術。傳統圖形比對技術為使用相關係數(Correlation coefficient)來作為相似度之衡量指標，此方法已廣泛用於圖形比對或瑕疵檢測中，然而相關係數應用在圖形比對上只提供單一指標作為評估依據，且對兩比對影像中異常區域的凸顯效果有不穩定的現象。
本研究方法概念主要利用標準影像與待測影像每一相同座標點的灰階值形成一個灰階對應圖，由此2D灰階圖形之分布形狀，能清楚觀察出標準影像與待測影像之差異。灰階對應圖中傳達了兩張影像對應關係資訊，可透過共變異矩(Covariance matrix)來描述其關係，並進一步利用共變異矩陣產生之多重指標，作為瑕疵檢測或圖形比對之相似度(Similarity)衡量標準。由於共變異矩陣所提供關於兩張比對影像相似程度之資訊較相關係數豐富且對瑕疵區域有較佳之凸顯效果，故應用於圖形比對時可達到穩定之比對效果。實驗中針對印刷電路板、液晶顯示器面板、晶圓、印刷字元等樣本進行測試，結果發現本研究方法應用於瑕疵檢測具有極佳的效果，故本研究提供一個穩定之瑕疵檢測方法。

關鍵字

機器視覺 ； 相關係數 ； 圖形比對 ； 相似度量測 ； 共變異矩陣

並列摘要

In this research, novel similarity measures are presented for automated defect inspection. Traditional normalized correlation approach has been extensively used as a similarity measure for pattern matching. However, it cannot provide good discrimination for detecting subtle defects in complicated images. The purpose of this study focuses on finding effective similarity measures, especially for defect detection applications.
The core idea of this study comes from conceptually constructing a gray-level corresponding map for two compared images. The x-axis and y-axis of the corresponding map are defined by the gray values of the reference image and the scene image, respectively. The pair-wise gray levels of each pixel coordinates in the images form a diagonal straight line in the corresponding map if the two compared images are identical. Any two compared images different to some extent will not have the shape of a line in the map. Eigenvalues and major-axis angle of the covariance matrix of the data points in the map are used as similarity measures to evaluate the difference between two compared images.
The proposed eignevalue-based similarity measures have better discrimination capability, and are more stable for defect detection application, compared to the normalized correlation. Experimental results on real industrial samples such as PCB, SMT, and printed characters have shown the efficacy of the proposed similarity measures.

並列關鍵字

Inspection ； Defect detection ； Normalized correlation ； Similarity measures ； Eigenvalues ； Covariance matrix

參考文獻

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