文件扫描时得到的图片可能会有倾斜并且周围带有白边如左图，想得到较好的效果如右图。
方案步骤：
1.查找轮廓找到感兴趣区域（带方向的矩形）
2.计算感兴趣区域的中心及角度
3.计算旋转矩阵并将图像旋转摆正
4.对摆正后的图像查找轮廓找到感兴趣区域（最小外接矩形）
5.从摆正后的图像中抠出感兴趣区域则得到最终效果图
#include<opencv2\opencv.hpp>
using namespace cv;
using namespace std;
void callback(int, void*);
int value = 40;
Mat src, gray,canny_img;
int main(int arc, char** argv) {
src = imread("2.jpg");
namedWindow("input", CV_WINDOW_AUTOSIZE);
imshow("input", src);
namedWindow("output", CV_WINDOW_AUTOSIZE);
createTrackbar("threshold", "output", &value, 2 * value, callback);
callback(0, 0);
waitKey(0);
return 0;
}
void callback(int, void*) {
cvtColor(src, gray, CV_BGR2GRAY);
Canny(gray, canny_img, value, 2 * value, 3);
imshow("output", canny_img);
//寻找轮廓
vector <vector<Point>>contours;
vector<Vec4i>hierarchy;
findContours(canny_img, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
//筛选轮廓
int minW = src.cols*0.5;
int minH = src.rows*0.5;
Mat draw = Mat::zeros(src.size(), CV_8UC3);
Mat dst;
for (int i = 0; i < contours.size(); i++) {
//寻找轮廓带方向的最小外接矩形（带方向即最小面积矩形）
RotatedRect minRect = minAreaRect(contours[i]);
if (minRect.size.width > minW && minRect.size.height > minH && minRect.size.width < (src.cols - 5)) {
//画出带方向的矩形
Point2f pts[4];
minRect.points(pts);
for (int j = 0; j < 4; j++) {
line(draw, pts[j], pts[(j + 1) % 4], Scalar(0, 255, 0), 2);
}
imshow("output2", draw);
//旋转变换
float degree = minRect.angle;
Point2f center = minRect.center;
Mat rotm = getRotationMatrix2D(center, degree, 1.0); //获取旋转矩阵
warpAffine(src, dst, rotm, src.size(), INTER_LINEAR, 0, Scalar(255, 255, 255));// 进行图像旋转
imshow("output3", dst);
}
}
//切边
Mat gray, binary;
cvtColor(dst, gray, CV_BGR2GRAY);
threshold(gray, binary, 60, 255, THRESH_BINARY|THRESH_OTSU );
vector <vector<Point>>contours2;
vector<Vec4i>hierarchy2;
Mat draw2 = Mat::zeros(src.size(), CV_8UC3);
findContours(binary, contours2, hierarchy2, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
for (int j = 0; j < contours2.size(); j++) {
Rect box = boundingRect(contours2[j]);
if (box.width > dst.cols*0.3 && box.height > dst.rows*0.3 && box.width<(src.cols-5)) {
rectangle(draw2, box, Scalar(0,255, 255), 2);
imshow("output4", draw2);
Mat result_img = dst(box);
imshow("output5", result_img);
}
}
}
