直接上代码吧：

#include "cv.h"
#include "highgui.h"

int slider_pos=70;//阈值

IplImage *image02 =0,*image03 = 0,*image04 = 0;
void process_image(int h);

int main(int argc ,char **argv)
{
	//const char *filename ="binaryGroup.bmp";
	const char *filename ="003.jpg";
	if ((image03 = cvLoadImage(filename,0))==0)//读入图像为灰度图像
	{
		return -1;
	}
	image02 = cvCloneImage(image03);
	image04 = cvCloneImage(image03);

	cvNamedWindow("Source",1);
	cvNamedWindow("Result",1);

	cvShowImage("Source",image03);

	cvCreateTrackbar("Threshold","Result",&slider_pos,255,process_image);

	process_image(0);

	cvWaitKey(0);
	cvSaveImage("1.jpg",image04);

	cvReleaseImage(&image02);
	cvReleaseImage(&image03);

	cvDestroyWindow("Source");
	cvDestroyWindow("Result");
	return 0;

}

//这个函数寻找出轮廓、用椭圆拟合画出
void process_image(int h)
{
	CvMemStorage *stor;
	CvSeq *cont;
	CvBox2D32f *box;
	CvPoint *PointArray;
	CvPoint2D32f *PointArray2D32f;

	stor = cvCreateMemStorage(0);
	cont = cvCreateSeq(CV_SEQ_ELTYPE_POINT,sizeof(CvSeq),sizeof(CvPoint),stor);

	cvThreshold(image03,image02,slider_pos,255,CV_THRESH_BINARY);

	cvFindContours(image02,stor,&cont,sizeof(CvContour),
		CV_RETR_LIST,CV_CHAIN_APPROX_NONE,cvPoint(0,0));

	cvZero(image02);
	cvZero(image04);

	//绘制所有轮廓并用椭圆拟合
	for (;cont;cont = cont ->h_next)
	{
		int i;
		int count= cont->total;//轮廓个数
		CvPoint center;
		CvSize size;

		/*个数必须大于6，这是cvFitEllipse_32f的要求*/
		if (count<6)
		{
			continue;
		}

		//分配内存给点集
		PointArray = (CvPoint *)malloc(count*sizeof(CvPoint));
		PointArray2D32f = (CvPoint2D32f*)malloc(count*sizeof(CvPoint2D32f));

		//分配内存给椭圆数据
		box = (CvBox2D32f *)malloc(sizeof(CvBox2D32f));

		//得到点集（这个方法值得借鉴）
		cvCvtSeqToArray(cont,PointArray,CV_WHOLE_SEQ);

		//将CvPoint点集转化为CvBox2D32f集合
		for (i=0;i<count;i++)
		{
			PointArray2D32f[i].x=(float)PointArray[i].x;
			PointArray2D32f[i].y=(float)PointArray[i].y;
		}

		//拟合当前轮廓
		cvFitEllipse(PointArray2D32f,count,box);

		//绘制当前轮廓
		cvDrawContours(image04,cont,CV_RGB(255,255,255),CV_RGB(255,255,255),
			0,1,8,cvPoint(0,0));

		//将椭圆数据从浮点转化为整数表示
		center.x = cvRound(box->center.x);
		center.y = cvRound(box->center.y);
		size.width = cvRound(box->size.width*0.5);
		size.height = cvRound(box->size.height*0.5);
		box->angle = -box->angle;

		//画椭圆
		cvEllipse(image04,center,size,box->angle,0,360,CV_RGB(0,0,255),1,CV_AA,0);

		free(PointArray);
		free(PointArray2D32f);
		free(box);
	}
	cvShowImage("Result",image04);
}

【OpenCV学习】椭圆拟合