提取ROI

 1.通过trackbar获取thresh最佳值

#include "head.h"

//  1.边缘检测 + 轮廓发现或者直线检测最大外接矩形
//  2.二值分割 + 形态学方法 + hough直线找最大外接矩形
void findROI(int, void*);
Mat src, grayimg, dst;
const char* output = "final";
int maxvalue = 255;
int thresh = 150;

void qiebian()
{
	src = imread("img/12.jpg");
	namedWindow(output, CV_WINDOW_AUTOSIZE);
	createTrackbar("threshold", output, &thresh, maxvalue, findROI);
	findROI(0, 0);
	waitKey(0);
}

void findROI(int ,void*)
{
	cvtColor(src, grayimg, COLOR_BGR2GRAY);
	Mat canny;
	Canny(grayimg, canny, thresh, thresh * 2, 3, false);
	vector<vector<Point>> contours;
	vector<Vec4i> hireachy;
	findContours(canny, contours, hireachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));

	int minw = src.cols*0.8;
	int minh = src.rows*0.8;
	RNG rng(12345);

	for (int i = 0; i < contours.size(); i++)
	{
		//将轮廓中所有点contours[i]转换成rect
		RotatedRect minRect = minAreaRect(contours[i]);
		if (minRect.size.width > minw && minRect.size.height > minh && minRect.size.width<(src.cols-5))
		{
			Point2f pts[4];
			minRect.points(pts);
			Scalar color = Scalar(rng.uniform(0,255), rng.uniform(0, 255), rng.uniform(0, 255));
			for (int j = 0; j < 4; j++)
			{
				line(src, pts[j], pts[(j + 1)%4], color, 2, 8, 0);
			}
		}
	}
	imshow(output, src);
}

2.确定thresh最佳值后直接提取感兴趣区域 

void qiebian()
{
	src = imread("img/12.jpg");
	cvtColor(src, grayimg, COLOR_BGR2GRAY);
	Canny(grayimg, grayimg, thresh, thresh * 2, 3, false);
	vector<vector<Point>> conts;
	vector<Vec4i> hireachy;
	int h = src.rows*0.8;
	int w = src.cols*0.8;
	findContours(grayimg, conts, hireachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
	for (int i = 0; i < conts.size(); i++)
	{
		RotatedRect rect = minAreaRect(conts[i]);
		if (rect.size.height>h && rect.size.width>w && rect.size.width<(src.cols-5))
		{
			Rect finalRect = rect.boundingRect();
			dst = src(finalRect);
			imshow(output, dst);
			break;
		}
	}
	waitKey(0);
}

3.旋转角度调整