尋找輪廓--OpenCV14

一般一個輪廓都對應一系列的點，也就是圖像中的一條曲線。其表示方法可能根據不同的情況有所不同。

可以利用 findContours()函數從二值圖像中查找輪廓。

 

CV_EXPORTS_W void findContours( InputArray image, OutputArrayOfArrays contours,
                              OutputArray hierarchy, int mode,
                              int method, Point offset = Point());

第一個參數，輸入圖像，需爲8位單通道圖像。

第二個參數 ，檢測到的輪廓，函數調用後的運算結果存在這裏

每個輪廓存儲爲一個點向量 ，即用point類型的vector表示

第三個參數爲可選擇的輸出參數，包含圖像的拓撲信息。每個輪廓contours[i]對應四個hierarchy元素

hierarchy[i][0]~hierarchy[i][3]，分別表示後一個輪廓，前一個輪廓，父輪廓，內嵌輪廓的索引編號。

如果沒有對應值，對應的hierarchy[i]設置爲負值

第四個參數 mode，輪廓索引方式

    /** retrieves only the extreme outer contours. It sets `hierarchy[i][2]=hierarchy[i][3]=-1` for
    all the contours. */
    RETR_EXTERNAL  = 0,
    /** retrieves all of the contours without establishing any hierarchical relationships. */
    RETR_LIST      = 1,
    /** retrieves all of the contours and organizes them into a two-level hierarchy. At the top
    level, there are external boundaries of the components. At the second level, there are
    boundaries of the holes. If there is another contour inside a hole of a connected component, it
    is still put at the top level. */
    RETR_CCOMP     = 2,
    /** retrieves all of the contours and reconstructs a full hierarchy of nested contours.*/
    RETR_TREE      = 3,

第五個參數 method爲輪廓的近似辦法

    /** stores absolutely all the contour points. That is, any 2 subsequent points (x1,y1) and
    (x2,y2) of the contour will be either horizontal, vertical or diagonal neighbors, that is,
    max(abs(x1-x2),abs(y2-y1))==1. */
    CHAIN_APPROX_NONE      = 1,
    /** compresses horizontal, vertical, and diagonal segments and leaves only their end points.
    For example, an up-right rectangular contour is encoded with 4 points. */
    CHAIN_APPROX_SIMPLE    = 2,
    /** applies one of the flavors of the Teh-Chin chain approximation algorithm @cite TehChin89 */
    CHAIN_APPROX_TC89_L1   = 3,
    /** applies one of the flavors of the Teh-Chin chain approximation algorithm @cite TehChin89 */
    CHAIN_APPROX_TC89_KCOS = 4

第六個參數 Point類型的offset ，每個輪廓點的可選偏移量，有默認值point（）。對ROI圖像中找出的輪廓，並要在整個圖像中進行分析時，這個參數就排上用場了。

 

findContours經常與drawContours配合使用，檢測到輪廓後使用drawContours繪製出來。

CV_EXPORTS_W void drawContours( InputOutputArray image, InputArrayOfArrays contours,
                              int contourIdx, const Scalar& color,
                              int thickness = 1, int lineType = LINE_8,
                              InputArray hierarchy = noArray(),
                              int maxLevel = INT_MAX, Point offset = Point() );

 

	threshold(GrayImg, GrayImg, 125, 255, 0);

	imshow("input img", GrayImg);
	
	Mat dstImg;
	dstImg = Mat::zeros(Img1.size(), Img1.type());

	vector<vector<Point>> contours; //存放輪廓的點
	vector<Vec4i> hierachy;  


	findContours(GrayImg, contours, hierachy, RETR_CCOMP, CHAIN_APPROX_SIMPLE);


	int index = 0;
	for (;index >= 0; index = hierachy[index][0])
	{
		Scalar color(rand() % 255, rand() % 255, rand() % 255);
        	drawContours(dstImg, contours,index, color, FILLED, LINE_AA, hierachy);
	}

	imshow("Output Img", dstImg);