利用包围轮廓和仿射变换进行图像倾斜校正

本文所展示的是利用OpenCV来进行图像的倾斜校正，由于图像背景复杂，需要旋转的角度未知，我们大致需要完成以下几个步骤：

对图像进行二值化处理，方便检测出目标的轮廓
计算图像的矩，绘制轮廓，并利用minAreaRect()函数寻找最小面积的包围矩形
计算旋转矩阵，并通过旋转矩阵来完成最终的倾斜校正

实现细节

代码如下：

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace cv;
using namespace std;
//空洞填充
void fillHole(const Mat srcBw, Mat &dstBw)
{
    Size m_Size = srcBw.size();
    Mat Temp = Mat::zeros(m_Size.height + 2, m_Size.width + 2, srcBw.type());//延展图像
    srcBw.copyTo(Temp(Range(1, m_Size.height + 1), Range(1, m_Size.width + 1)));
    cv::floodFill(Temp, Point(0, 0), Scalar(255));
    Mat cutImg;//裁剪延展的图像
    Temp(Range(1, m_Size.height + 1), Range(1, m_Size.width + 1)).copyTo(cutImg);
    dstBw = srcBw | (~cutImg);
}
int main()
{
    Mat src = imread("rotImage.jpg");
    if (!src.data)
    {
        printf("读取图片错误！ \n"); 
        return false;
    }
    imshow("原图像", src);
    Mat src1 = src.clone();
    //图像预处理
    Mat dst, gray, edge;
    dst.create(src1.size(), src1.type());
    cvtColor(src1, gray, COLOR_BGR2GRAY);
    blur(gray, edge, Size(3, 3));
    Mat bw;
    cv::threshold(edge, bw, 120, 250, 0);
    //填充图像
    Mat bwFill;
    fillHole(bw, bwFill);
    imshow("二值化处理后的图像", bwFill);
    //找到轮廓
    vector<vector<Point>> contours;
    vector<Vec4i> hierarchy;
    findContours(bwFill, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);
    //计算矩
    vector<Moments> mu(contours.size());
    for (unsigned int i = 0; i < contours.size(); i++)
    {
    mu[i] = moments(contours[i], false);
    }
    //计算中心矩
    vector<Point2f> mc(contours.size());
    for (unsigned int i = 0; i < contours.size(); i++)
    {
    mc[i] = Point2f(static_cast<float>(mu[i].m10 / mu[i].m00), static_cast<float>(mu[i].m01 / mu[i].m00));
    }
    //绘制轮廓
    Mat drawing = Mat::zeros(bwFill.size(), CV_8UC3);
    RNG g_rng(12345);
    for (unsigned int i = 0; i< contours.size(); i++)
    {
    Scalar color = Scalar(g_rng.uniform(0, 255), g_rng.uniform(0, 255), g_rng.uniform(0, 255));//随机生成颜色值
    drawContours(drawing, contours, i, color, 2, 8, hierarchy, 0, Point());//绘制外层和内层轮廓
    circle(drawing, mc[i], 4, color, -1, 8, 0);//绘制圆
    }
    //绘制外框矩形
    RotatedRect box;
    Point2f vertex[4];
    for (unsigned int i = 0; i < contours.size(); i++)
    {
        box = minAreaRect(Mat(contours[i]));//寻找最小面积的包围矩形
        box.points(vertex);
        for (int i = 0; i < 4; i++)
            line(drawing, vertex[i], vertex[(i + 1) % 4], Scalar(100, 200, 211), 2, CV_AA);//绘制出最小面积的包围矩形
    }
    imshow("绘制的矩形框", drawing);
    cout <<"需要校正的角度为："<< box.angle;
    // 计算旋转矩阵
    Mat rotMat, rotateImage;
    rotMat = getRotationMatrix2D(box.center, box.angle,1);
    // 旋转图像
    warpAffine(src, rotateImage, rotMat, src.size());
    // 显示到窗口中
    imshow("校正后的图像", rotateImage);
    waitKey(0);
    return 0;
}