影像處理應用於矩陣LED瑕疵檢測之研究

Abstract

矩陣發光二極體（Matrix Light Emitting Diode, Matrix LED）是業界應用最廣泛的LED材料之一。因為矩陣LED是個低單價的產品，加上檢測機台成本太高，使得廠商購買意願降低，所以矩陣LED瑕疵缺陷仍然由人工進行檢測。隨著人工成本提升和人工檢測的不穩定性，我們需要應用自動光學檢測(Automated Optical Inspection, AOI)解決矩陣LED瑕疵檢測的問題。在這本論文研究中，我們提出了一套有效的矩陣LED檢測系統。該系統提供三種檢測，第一為表面刮傷瑕疵、第二為RGB亮暗點檢測、第三為使用支援向量機(Support Vector Machine, SVM)進行亮暗點分析。 在表面刮傷瑕疵檢測主要由SURF (Speeded-Up Robust Features)特徵匹配結合透視變換進行圖像校正，然後在輪廓檢測部分本文使用FindContours函式，接著找出瑕疵邊緣使用Canny邊緣檢測，該方法的準確度可達98.00％，檢測每顆矩陣LED需花2.95秒。 RGB亮暗點檢測使用ROI擷取每顆LED後，使用cvAvgSdv函式計算R、G、B平均值，首先與前一顆LED進行G值的比較，將有色差LED檢測出來，最後與制訂範圍進行判斷，該方法的準確度可達到98.00%，實驗結果顯示，檢測每顆矩陣LED需花0.01秒。 最後，使用SVM結合HOG進行圖像分類，解決矩陣LED亮暗點的問題，其準確率可達98.33％，執行速度上，檢測每顆矩陣LED需花0.38秒。實驗結果顯示，所提出的方法是有效的，並勝過以前的方法。The Matrix Light Emitting Diode (Matrix LED) is one of the most widely used LED material in the industry. With a low unit price, Matrix LED manufacturers don't have much incentive to invest in expensive inspection machines, so the job of detecting defects still relies on manual work. With the rise of the labor cost and the instability of the manual inspection quality, it is needed to apply Automatic Optical Inspection (AOI). In this study, we propose an effective AOI system for Matrix LED. The system provides three defect inspections, Surface defects, RGB Bright/Dark spot, and SVM Bright/Dark spot analysis. In this paper, Surface defects detection is mainly done through image correction by SURF feature matching and Perspective Transformation. Then we find contour with the findCoutours function and finally use the Canny edge detection to detect defect edges. This technique has a 98.00% accuracy and it takes about 2.95 seconds to examine each Matrix LED. For RGB Bright/Dark spot detection, we use ROI to capture each LED, obtain mean RGB values with the cvAvgSdv function, see if they fall within defined ranges and compare the G value with the previous LED to locate LEDs with color differences. This technique has a 98.00% accuracy and it takes about 0.01 seconds to examine each LED Matrix. Lastly, we combine SVM with HOG for image classification to remedy Bright/Dark spots. This procedure has a 98.33% accuracy and it takes about 0.38 seconds to examine each LED Matrix. Experimental results show that the proposed methods are effective and outperform the previous methods.