已有一張圖片，找到裡面需要的矩形。

程式碼

#include <opencv2/opencv.hpp>
#include <opencv2/opencv_modules.hpp>
#include <opencv2/nonfree/features2d.hpp>
#include <opencv2/nonfree/nonfree.hpp>
#include <opencv2/core/Core.hpp>
#include <stdio.h>
#include <vector>
#include <algorithm>
 

using namespace cv;

typedef struct 
{
    cv::Rect rect;
    double distance;
    int countInRange;
} rectPointType;

bool sortFun(const rectPointType& r1, const rectPointType& r2)
{
    return (r1.countInRange > r2.countInRange);
}

int main()
{
    Mat imgSrc = cv::imread("2.png", 1);

    cv::Size sz = imgSrc.size();
    if
 
 (sz.width > 0)
    {
        imshow("pic", imgSrc);
    }

    Mat imgBlur;
    blur(imgSrc, imgBlur, cv::Size(7, 7));

    Mat imgGray;
    cvtColor(imgBlur, imgGray, CV_BGR2GRAY);

    Mat canny_output;
    int thresh = 10;
    Canny(imgGray, canny_output, thresh, thresh * 2, 3);

    int dilation_type = MORPH_CROSS;
    int
 
 dilation_size = 2;
    Mat element = getStructuringElement(dilation_type,
        Size(2 * dilation_size + 1, 2 * dilation_size + 1),
        Point(dilation_size, dilation_size));

    dilate(canny_output, canny_output, element);

    imshow("pic_canny", canny_output);


    vector<vector<Point> > countours;
    vector<Vec4i> hierarchy;

    /// Find contours
    findContours(canny_output, countours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0));

    vector<vector<Point> > vecApproxOut;
    vector<rectPointType> vecRect;
    for (int i = 0; i < countours.size(); i++)
    {
        vector<Point> approxOut;
        approxPolyDP(Mat(countours[i]), approxOut, arcLength(Mat(countours[i]), true) * 0.01, true);

        if ((approxOut.size() < 4) || (approxOut.size() > 10))
        {
            continue;
        }

        double area = contourArea(approxOut);
        if ((area < 1000) || (area >10000))
        {
            continue;
        }

        Rect rect;
        rect = boundingRect(approxOut);

        double t = ((float)rect.height / ((float)rect.width));
        std::cout << "t " << t << std::endl;
        if ((t < 0.8) || (t > 1.3))
        {
            continue;
        }

        rectPointType rectPoint;
        rectPoint.rect = rect;
        rectPoint.distance = 0.0f;

        vecRect.push_back(rectPoint);
    }

    for (int index = 0; index < vecRect.size(); index++)
    {
        rectPointType now_rect = vecRect.at(index);
        int countInRange = 0;
        for (int i = 0; i < vecRect.size(); i++)
        {
            double x = now_rect.rect.x - vecRect.at(i).rect.x;
            double y = now_rect.rect.y - vecRect.at(i).rect.y;
            double dis = x*x + y*y;
            std::cout << "index " << index << " dis " << dis << std::endl;
            if (dis < 60000)
            {
                countInRange++;
            }
        }
        vecRect.at(index).countInRange = countInRange;
    }

    std::sort(vecRect.begin(), vecRect.end(), sortFun);

    vector<Point> pointBox;

    for (int i = 0; i < vecRect.size(); i++)
    {
        if (vecRect.at(i).countInRange > 8)
        {
            Point p1;
            Point p2;
            Point p3;
            Point p4;

            p1.x = vecRect.at(i).rect.x;
            p1.y = vecRect.at(i).rect.y;

            p2.x = vecRect.at(i).rect.x + vecRect.at(i).rect.height;
            p2.y = vecRect.at(i).rect.y;

            p3.x = vecRect.at(i).rect.x + vecRect.at(i).rect.height;
            p3.y = vecRect.at(i).rect.y + vecRect.at(i).rect.width;

            p4.x = vecRect.at(i).rect.x;
            p4.y = vecRect.at(i).rect.y + vecRect.at(i).rect.width;

            pointBox.push_back(p1);
            pointBox.push_back(p2);
            pointBox.push_back(p3);
            pointBox.push_back(p4);
        }
    }

    Rect rectBox;
    rectBox = boundingRect(pointBox);

    line(imgSrc, Point(rectBox.x, rectBox.y), Point(rectBox.x + rectBox.width, rectBox.y), cvScalar(0, 0, 255), 4);
    line(imgSrc, Point(rectBox.x + rectBox.width, rectBox.y), Point(rectBox.x + rectBox.width, rectBox.y + rectBox.height), cvScalar(0, 255, 0), 4);
    line(imgSrc, Point(rectBox.x + rectBox.width, rectBox.y + rectBox.height), Point(rectBox.x, rectBox.y + rectBox.height), cvScalar(255, 0, 0), 4);
    line(imgSrc, Point(rectBox.x, rectBox.y + rectBox.height), Point(rectBox.x, rectBox.y), cvScalar(0, 255, 255), 4);

    imshow("imgSrc", imgSrc);
    waitKey(0);
    return 0;
}

結果

矩形